Motive power system, transportation apparatus, and power transmission method

ABSTRACT

A motive power system includes a first energy storage, a second energy storage, an actuator, an internal combustion engine, a power transmission circuit, and circuitry. The circuitry is configured to control the power transmission circuit in a charge-depleting mode such that the first energy storage supplies to the actuator a first electric energy that is stored in the first energy storage with a first charge rate range and the second energy storage supplies to the actuator a second electric energy that is stored in the second energy storage with a second charge rate range. The first charge rate range is larger than the second charge rate range.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2016-066920, filed Mar. 29, 2016, entitled“Motive Power System, Transportation Apparatus, and Power TransmissionMethod for Motive Power System.” The contents of this application areincorporated herein by reference in their entirety.

BACKGROUND 1. Field

The present disclosure relates to a motive power system, atransportation apparatus, and a power transmission method.

2. Description of the Related Art

Motive power systems, as disclosed in Japanese Unexamined PatentApplication Publication Nos. 2014-15113 and 2015-70726, for example, areknown in the related art. Japanese Unexamined Patent ApplicationPublication No. 2014-15113 discloses a technique for a hybrid vehicleincluding two energy storage devices. In this technique, two modes areprovided to enable wide-range travel in a travel mode of an electricvehicle (EV). One of the modes is a mode in which the voltage of alower-capacity energy storage device is boosted so that a voltage fordriving a motor generator when an engine is started becomes equal to thevoltage of a higher-capacity energy storage device. The other mode is amode in which the voltage of the lower-capacity energy storage device isboosted so that the voltage for driving the motor generator when theengine is started becomes equal to a voltage higher than the voltage ofthe higher-capacity energy storage device.

Japanese Unexamined Patent Application Publication No. 2015-70726discloses a technique for a hybrid vehicle including two energy storagedevices, for supplying power from only a high-capacity energy storagedevice when the required output for power is less than a threshold andsupplying power from both energy storage devices when the requiredoutput for power is greater than the threshold.

The hybrid vehicles disclosed in Japanese Unexamined Patent ApplicationPublication Nos. 2014-15113 and 2015-70726 can be each regarded as, moregenerally, a motive power system that includes an internal combustionengine and an actuator as sources of motive power for driving a drivenload and that includes two energy storage devices as power supplies forthe actuator.

SUMMARY

According to a first aspect of the present invention, a motive powersystem includes a first energy storage, a second energy storage, anactuator, an internal combustion engine, a power transmission circuit,and circuitry. The first energy storage has a first power density and afirst energy density. The second energy storage has a second powerdensity higher than the first power density, and a second energy densitylower than the first energy density. The actuator provides motive forceto a load with electric power supplied from at least one of the firstenergy storage and the second energy storage. The internal combustionengine provides motive force to the load. The actuator is connected tothe first energy storage and to the second energy storage via the powertransmission circuit to supply electric power to the actuator. Thecircuitry is configured to control the power transmission circuit andthe internal combustion engine such that only the actuator providesmotive force to the load in a charge-depleting mode and such that theinternal combustion engine and the actuator provide motive force to theload in a charge-sustaining mode. The circuitry is configured to controlthe power transmission circuit in the charge-depleting mode such thatthe first energy storage supplies to the actuator a first electricenergy that is stored in the first energy storage with a first chargerate range and the second energy storage supplies to the actuator asecond electric energy that is stored in the second energy storage witha second charge rate range. The first charge rate range is larger thanthe second charge rate range.

According to a second aspect of the present invention, a motive powersystem includes a first energy storage, a second energy storage, anactuator, an internal combustion engine, a power transmission circuit,and circuitry. The first energy storage has a first power density and afirst energy density. The second energy storage has a second powerdensity higher than the first power density, and a second energy densitylower than the first energy density. The actuator provides motive forceto a load with electric power supplied from at least one of the firstenergy storage and the second energy storage. The internal combustionengine provides motive force to the load. The actuator is connected tothe first energy storage and to the second energy storage via the powertransmission circuit to supply electric power to the actuator. Thecircuitry is configured to control the power transmission circuit andthe internal combustion engine such that only the actuator providesmotive force to the load in a charge-depleting mode and such that theinternal combustion engine and the actuator provide motive force to theload in a charge-sustaining mode. The circuitry is configured to controlthe power transmission circuit in the charge-sustaining mode such thatthe first energy storage supplies to the actuator a first electricenergy that is stored in the first energy storage with one charge raterange and the second energy storage supplies to the actuator a secondelectric energy that is stored in the second energy storage with ananother charge rate range, the another charge rate range being largerthan the one charge rate range.

According to a third aspect of the present invention, a powertransmission method for a motive power system including a first energystorage having a first power density and a first energy density, asecond energy storage having a second power density higher than thefirst power density and a second energy density lower than the firstenergy density, an actuator to provide motive force to a load withelectric power supplied from at least one of the first energy storageand the second energy storage, and an internal combustion engine toprovide motive force to the load, the power transmission method includesperforming power transmission such that only the actuator providesmotive force to the load in a charge-depleting mode and such that theinternal combustion engine and the actuator provide motive force to theload in a charge-sustaining mode. The power transmission method includesperforming power transmission in the charge-depleting mode such that thefirst energy storage supplies to the actuator a first electric energythat is stored in the first energy storage with a first charge raterange and the second energy storage supplies to the actuator a secondelectric energy that is stored in the second energy storage with asecond charge rate range, the first charge rate range being larger thanthe second charge rate range.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 illustrates an overall configuration of a motive power systemaccording to an embodiment disclosed herein.

FIG. 2 conceptually illustrates how the respective capacities of a firstenergy storage device and a second energy storage device are allocatedfor use.

FIG. 3 is a flowchart illustrating a main routine process executed by acontrol device.

FIG. 4 illustrates a map used in a control process when power issupplied to an electric motor in a charge-depleting (CD) mode.

FIG. 5 is a flowchart illustrating the control process when power issupplied to the electric motor in the CD mode.

FIG. 6 is a flowchart illustrating the control process when power issupplied to the electric motor in the CD mode.

FIG. 7 is a flowchart illustrating the control process when power issupplied to the electric motor in the CD mode.

FIG. 8 is a graph exemplifying the relationship between respectivepercentage shares for the first energy storage device and the secondenergy storage device and amounts of heat generation.

FIG. 9 illustrates a map used in a control process during regenerativeoperation of the electric motor in the CD mode.

FIG. 10 is a flowchart illustrating a control process duringregenerative operation of the electric motor in the CD mode.

FIG. 11 illustrates a map used in a control process when power issupplied to the electric motor in a first charge-sustaining (CS) mode.

FIG. 12 is a flowchart illustrating a control process when power issupplied to the electric motor in the first CS mode.

FIG. 13 is a flowchart illustrating a control process when power issupplied to the electric motor in the first CS mode.

FIG. 14 illustrates a map used in a control process during regenerativeoperation of the electric motor in the first CS mode.

FIG. 15 is a flowchart illustrating a control process duringregenerative operation of the electric motor in the first CS mode.

FIG. 16 illustrates a map used in a control process when power issupplied to the electric motor in a second CS mode.

FIG. 17 is a flowchart illustrating a control process when power issupplied to the electric motor in the second CS mode.

FIG. 18 illustrates a map used in a control process during regenerativeoperation of the electric motor in the second CS mode.

FIG. 19 is a flowchart illustrating a control process duringregenerative operation of the electric motor in the second CS mode.

FIG. 20 is a graph exemplifying patterns in which the respective SOCs ofthe first energy storage device and the second energy storage devicechange over time.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

An embodiment of the present disclosure will be described hereinafterwith reference to FIGS. 1 to 20. Referring to FIG. 1, a motive powersystem 1 according to this embodiment is a system mounted in a vehicle(more specifically, a hybrid vehicle) that is an example of atransportation apparatus.

The motive power system 1 includes an internal combustion engine 2, anelectric motor 3, an electric generator 4, a first energy storage device5, a second energy storage device 6, a power transmission circuit unit7, and a control device 8. The internal combustion engine 2 and theelectric motor 3 are capable of generating motive power for driving adrive wheel DW, which serves as a driven load, to rotate. The firstenergy storage device 5 and the second energy storage device 6 serve aspower supplies for the electric motor 3. The power transmission circuitunit 7 performs power transmission among the electric motor 3, theelectric generator 4, the first energy storage device 5, and the secondenergy storage device 6. The control device 8 has a function ofcontrolling the operation of the motive power system 1.

The internal combustion engine 2 transmits motive power generated byfuel combustion to the drive wheel DW via an appropriate powertrain todrive the drive wheel DW to rotate. The powertrain in the motive powersystem 1 in the illustrated example is configured to transmit motivepower generated by the internal combustion engine 2 from an output shaft2 a of the internal combustion engine 2 to the drive wheel DW via aclutch 11 and a plurality of gears 12, 13, 14, and 15 in sequence. Theclutch 11 is selectively operable between a connected state for makingtransmission of motive power feasible and a disconnected state fordisconnecting transmission of motive power.

The electric motor 3 corresponds to an actuator according to theembodiments disclosed herein. The electric motor 3 transmits motivepower generated through the power-running operation when supplied withpower to the drive wheel DW via an appropriate powertrain to drive thedrive wheel DW to rotate. The powertrain in the motive power system 1 inthe illustrated example is configured to transmit motive power generatedby the electric motor 3 from an output shaft 3 a of the electric motor 3to the drive wheel DW via the plurality of gears 16, 13, 14, and 15 insequence.

The electric motor 3 is also capable of performing, in addition to thepower-running operation, a regenerative operation for outputtingregenerative power by using the kinetic energy of the vehicle which istransmitted from the drive wheel DW.

While a single drive wheel DW is illustrated in FIG. 1 as arepresentative example, a plurality of drive wheels DW are present andmotive power is transmitted from the internal combustion engine 2 or theelectric motor 3 to the plurality of drive wheels DW via a powertrainincluding a differential gear apparatus (not illustrated).

The electric generator 4 is an electric generator configured such that arotating shaft 4 a of the electric generator 4 is driven to rotate byusing the motive power of the internal combustion engine 2, therebybeing able to output generated power. The rotating shaft 4 a of theelectric generator 4 is connected to the output shaft 2 a of theinternal combustion engine 2 via an appropriate powertrain so as torotate in association with the output shaft 2 a of the internalcombustion engine 2. The powertrain in the motive power system 1 in theillustrated example is configured to transmit motive power between theoutput shaft 2 a and the rotating shaft 4 a via two gears 17 and 18, forexample.

In this embodiment, the electric generator 4 further has a function ofan actuator (starter motor) for starting the internal combustion engine2 in addition to the function of an electric generator. That is, poweris supplied to the electric generator 4 to allow the electric generator4 to operate as an electric motor. The motive power of the electricgenerator 4, which serves as an electric motor, is transmitted from therotating shaft 4 a to the output shaft 2 a of the internal combustionengine 2, thereby driving the output shaft 2 a to rotate.

For additional explanation, the powertrain between the internalcombustion engine 2 or the electric motor 3 and the drive wheel DW andthe powertrain between the internal combustion engine 2 and the electricgenerator 4 are not limited to those having the configurationexemplified in FIG. 1 and various configurations are available.

These powertrains may include, for example, components other than gearsfor transmission of motive power, for example, pulleys and belts orsprockets and chains, and may also include gearboxes.

The output shaft 3 a of the electric motor 3 may be coupled coaxiallydirectly to or integrated with any rotating shaft in the powertrainbetween the clutch 11 and the drive wheel DW, for example.

The powertrain between the electric motor 3 and the drive wheel DW orthe powertrain between the internal combustion engine 2 and the electricgenerator 4 may include a clutch.

The motive power system 1 may include, besides the electric generator 4,an actuator for starting the internal combustion engine 2.

The first energy storage device 5 and the second energy storage device 6are energy storage devices chargeable by an external power supplythrough a charging device (not illustrated) included in the vehicle. Thefirst energy storage device 5 and the second energy storage device 6have different characteristics.

Specifically, the first energy storage device 5 is an energy storagedevice having a higher energy density than the second energy storagedevice 6. The energy density is an amount of electrical energy storableper unit weight or unit volume. The first energy storage device 5 may beformed of, for example, a lithium-ion battery.

The second energy storage device 6 is an energy storage device having ahigher power density than the first energy storage device 5. The powerdensity is an amount of electricity that can be output per unit weightor unit volume (an amount of electrical energy per unit time or anamount of charge per unit time). The second energy storage device 6 maybe formed of, for example, a lithium-ion battery, a nickel-hydrogenbattery, or a capacitor.

The first energy storage device 5 with relatively high energy density iscapable of storing a greater amount of electrical energy than the secondenergy storage device 6. The first energy storage device 5 has acharacteristic in which steady discharge with less occurrence of changesin the output of the first energy storage device 5, rather thandischarge with frequent occurrence of changes in the output of the firstenergy storage device 5, suppresses the progression of deterioration ofthe first energy storage device 5.

The first energy storage device 5 further has lower resistance todeterioration due to charging (in particular, charging at high rates)than the second energy storage device 6 (i.e., deterioration of thefirst energy storage device 5 caused by charging is more likely toprogress than that of the second energy storage device 6).

The second energy storage device 6 with relatively high power densityhas lower internal resistance (impedance) than the first energy storagedevice 5, and is thus able to instantaneously output high power. Thesecond energy storage device 6 has a characteristic in which thedischarging or charging of the second energy storage device 6 with thecharge rate being kept within an approximately middle range, rather thanthe discharging or charging of the second energy storage device 6 withthe charge rate being biased toward the high-capacity side or thelow-capacity side, suppresses the progression of deterioration of thesecond energy storage device 6. More specifically, the second energystorage device 6 has a characteristic in which the more the charge rateincreases or decreases toward the high-capacity side or the low-capacityside with respect to the approximately middle range, the more likely theprogression of deterioration of the second energy storage device 6 is tooccur.

The charge rate of each of the energy storage devices 5 and 6 is theratio of the remaining capacity to the full charge capacity. In thefollowing, the charge rate is sometimes referred to as SOC (state ofcharge). In addition, the SOC of the first energy storage device 5 issometimes referred to as the first SOC and the SOC of the second energystorage device 6 as the second SOC.

In this embodiment, the power transmission circuit unit 7 includes aninverter 21 connected to the electric motor 3, an inverter 22 connectedto the electric generator 4, a voltage converter 23 connected to thefirst energy storage device 5, and a voltage converter 24 connected tothe second energy storage device 6.

The inverters 21 and 22 are known circuits each having a switchingelement controlled by a duty signal to convert power from one ofdirect-current (DC) power and alternating-current (AC) power to theother.

The inverter 21 on the electric motor 3 side is capable of performingcontrol to, during the power-running operation of the electric motor 3,convert DC power input from the voltage converter 23 or 24 into AC powerand output the AC power to the electric motor 3, and is also capable ofperforming control to, during the regenerative operation of the electricmotor 3, convert AC power (regenerative power) input from the electricmotor 3 into DC power and output the DC power to the voltage converter23 or 24.

The inverter 22 on the electric generator 4 side is capable ofperforming control to, during the power generation operation of theelectric generator 4, convert AC power (generated power) input from theelectric generator 4 into DC power and output the DC power to thevoltage converter 23 or 24, and is also capable of performing controlto, when the electric generator 4 is driven as an actuator for startingthe internal combustion engine 2, convert DC power input from thevoltage converter 23 or 24 into AC power and output the AC power to theelectric generator 4.

The voltage converters 23 and 24 are known circuits (switching-typeDC/DC converters) each having a switching element controlled by a dutysignal to convert (boost or step down) the voltage of the DC power. Eachof the voltage converters 23 and 24 is capable of variably controllingthe voltage conversion ratio (boosting ratio or step-down ratio), and isalso capable of performing bidirectional power transmission (powertransmission during the discharging of the corresponding one of theenergy storage devices 5 and 6 and power transmission during thecharging of the corresponding one of the energy storage devices 5 and6).

The control device 8 is constituted by an electronic circuit unitincluding a central processing unit (CPU), a random access memory (RAM),a read-only memory (ROM), an interface circuit, and so on. The controldevice 8 may be constituted by a plurality of electronic circuit unitsthat are capable of communicating with each other.

The control device 8 includes, as functions implemented by a hardwareconfiguration to be mounted therein or by a program (softwareconfiguration) to be installed therein, an internal combustion engineoperation controller 31, a power transmission controller 32, a clutchcontroller 33, and a brake controller 34. The internal combustion engineoperation controller 31 controls the operation of the internalcombustion engine 2. The power transmission controller 32 controls thepower transmission circuit unit 7 (and therefore controls the operationof the electric motor 3 and the electric generator 4). The clutchcontroller 33 controls switching between operating states of the clutch11. The brake controller 34 controls a brake device (not illustrated) ofthe vehicle.

The control device 8 receives input of various sensing data asinformation necessary to implement the functions described above. Thesensing data includes, for example, data indicating the amount ofoperation of the accelerator pedal of the vehicle, the amount ofoperation of the brake pedal, the vehicle speed, the rotational speed ofthe output shaft 2 a of the internal combustion engine 2, the rotationalspeed of the output shaft 3 a of the electric motor 3, the rotationalspeed of the rotating shaft 4 a of the electric generator 4, and therespective detected values of the first SOC and the second SOC.

The control device 8 may include a function of an SOC detector thatdetects (estimates) the first SOC and the second SOC. In this case, thecontrol device 8 receives input of sensing data for estimating the firstSOC and the second SOC (for example, data indicating detected values ofthe voltage, current, temperature, and the like of the energy storagedevices 5 and 6) instead of sensing data indicating the respectivedetected values of the first SOC and the second SOC.

A specific description will now be given of a control process for thecontrol device 8.

Overview of Control Process for Control Device 8

First, a description will be given of an overview of a control processexecuted by the control device 8. The control process executed by thecontrol device 8 is broadly categorized into two types: a controlprocess for a charge-depleting (CD) mode and a control process for acharge-sustaining (CS) mode. The CD mode and the CS mode representoperation types of the motive power system 1 when the vehicle istraveling.

In this embodiment, the CD mode is a mode in which the motive power ofthe electric motor 3, out of the internal combustion engine 2 and theelectric motor 3, is usable as motive power for driving the drive wheelDW (as motive power for propelling the vehicle).

In the CD mode in this embodiment, the stored energy of the first energystorage device 5, out of the first energy storage device 5 and thesecond energy storage device 6, is used as the primary power sourceenergy for the electric motor 3 to perform the power-running operationof the electric motor 3.

In the CD mode in this embodiment, additionally, the internal combustionengine 2 remains at rest (the operation of the internal combustionengine 2 is disabled).

In this embodiment, in contrast, the CS mode is a mode in which themotive power of the internal combustion engine 2 and the motive power ofthe electric motor 3 are usable as motive power for driving the drivewheel DW. More specifically, the CS mode is a mode in which the motivepower of the internal combustion engine 2 is usable as primary motivepower for driving the drive wheel DW and the motive power of theelectric motor 3 is usable as auxiliary motive power for driving thedrive wheel DW.

The CS mode in this embodiment is divided into a first CS mode and asecond CS mode. In the first CS mode, the power in the second energystorage device 6, out of the first energy storage device 5 and thesecond energy storage device 6, is used as primary power source energyfor the power-running operation of the electric motor 3 and the power inthe second energy storage device 6 is used to charge (or is transferredto) the first energy storage device 5, if necessary, to graduallyrestore the SOC of the first energy storage device 5 (i.e., the firstSOC). In the second CS mode, the power in the first energy storagedevice 5, out of the first energy storage device 5 and the second energystorage device 6, is used as primary power source energy for thepower-running operation of the electric motor 3 and the generated powerof the electric generator 4 is used to charge the second energy storagedevice 6 to restore the SOC of the second energy storage device 6 (i.e.,the second SOC).

The control process in the first CS mode and the control process in thesecond CS mode are alternately executed so as to place the total chargeand discharge of the first energy storage device 5 and the second energystorage device 6 in balance as appropriate. As a result of repeating thecontrol process in the first CS mode and the control process in thesecond CS mode or as a result of plug-in charging with an externalelectric power system, the SOC of the first energy storage device 5 isrestored to some extent. Then, the mode of the control process isreturned from the CS mode to the CD mode.

A pattern indicating how the respective stored energies of the firstenergy storage device 5 and the second energy storage device 6 are usedin this embodiment will now be described with reference to FIG. 2.

In this embodiment, as depicted in a left percentage bar chart in FIG.2, a capacity (stored energy) of the range less than or equal to B1a (%)out of the full charge capacity (100% SOC) of the first energy storagedevice 5 is allocated as a capacity usable for power supply to theelectric motor 3. B1a (%) is set to represent a charge rate slightlyless than 100% with consideration given to a detection error of thefirst SOC, an error of charge control, or the like.

A capacity of the range of B1a (%) to Bib (%) is allocated as a capacityused for power supply to the electric motor 3 in the CD mode, and therange less than or equal to B1b (%) is allocated as a range thatincludes a capacity usable for power supply to the electric motor 3 inthe CS mode in an auxiliary manner. B1b (%) is set to represent an SOCclose to 0%.

The range less than or equal to Bib (%) includes, in addition to thecapacity usable for power supply to the electric motor 3 in the CS mode,margins that take into account a detection error of the first SOC or thelike.

In this manner, a range that occupies a large proportion (the range ofB1a (%) to B1b (%)) of the full charge capacity of the first energystorage device 5 is allocated as a capacity used for power supply to theelectric motor 3 in the CD mode.

In this embodiment, as depicted in a right percentage bar chart in FIG.2, a capacity of the range of B2a (%) to B2b (%) out of the full chargecapacity (100% SOC) of the second energy storage device 6 is allocatedas a dedicated capacity usable for power supply to the electric motor 3in the CD mode, and a capacity of the range of B2b (%) to B2c (%) isallocated as a capacity usable for power supply to the electric motor 3in the CS mode.

In this embodiment, part of the capacity of the range of B2b (%) to B2c(%) is also usable in the CD mode. Note that the capacity of the rangeof B2b (%) to B2c (%) is a capacity which is temporarily usable in theCD mode and which can basically be replenished, after part of thecapacity has been used for power supply to the electric motor 3, by thefirst energy storage device 5 by the amount used.

To minimize the progression of deterioration of the second energystorage device 6, it is preferable to discharge or charge the secondenergy storage device 6 when the second SOC is an SOC near anintermediate value. Accordingly, B2b (%) is set to approximately anintermediate SOC, B2a (%) is set to a value larger than B2b (%) to suchan extent that B2a (%) is not too close to 100%, and B2c (%) is set to avalue smaller than B2b (%) to such an extent that B2c (%) is not tooclose to 0%.

The range less than or equal to B2c (%) is allocated as a range thatincludes power for starting the internal combustion engine 2 (powerusable for power supply to the electric generator 4 serving as a starteractuator.

In this embodiment, when the internal combustion engine 2 is started,the second energy storage device 6 supplies power to the electricgenerator 4 and the power in the first energy storage device 5 is notused for power supply to the electric generator 4. This eliminates theneed for the first energy storage device 5 to reserve power for startingthe internal combustion engine 2.

This can increase the SOC range of the first energy storage device 5which is allocated as a capacity range for power supply to the electricmotor 3 in the CD mode. That is, in the CD mode in which fuelconsumption of the internal combustion engine 2 does not occur or issuppressed, the drivable range of the vehicle is increased and theenvironmental performance of the motive power system 1 is improved.Additionally, instantaneous power supply to the starter actuator (inthis embodiment, the electric generator 4), which is required to startthe internal combustion engine 2, is undertaken by the second energystorage device 6. This can favorably suppress the progression ofdeterioration of the first energy storage device 5.

As illustrated in FIG. 2, in the CD mode, the SOC range (of B1a (%) toBib (%)) of the first energy storage device 5 usable for power supply tothe electric motor 3 is larger than the SOC range (of B2a (%) to B2b(%)) of the second energy storage device 6 usable for power supply tothe electric motor 3.

Thus, in the CD mode, the power in the first energy storage device 5 canbe primarily used to perform the power-running operation of the electricmotor 3. In addition, the power in the second energy storage device 6can also be used in an auxiliary manner, if necessary, to perform thepower-running operation of the electric motor 3.

In particular, there is no need for the first energy storage device 5 toreserve power for starting the internal combustion engine 2. This makesit possible to maximize the SOC range (of B1a (%) to Bib (%)) usable forpower supply to the electric motor 3 in the CD mode.

As a result, in the CD mode in which only the motive power of theelectric motor 3 is used to propel the vehicle, the period during whichpower can be continuously supplied to the electric motor 3, andtherefore the drivable range of the vehicle in the CD mode in which fuelconsumption of the internal combustion engine 2 does not occur or issuppressed, can be maximized and the environmental performance of thevehicle can be improved.

In the CS mode, in contrast, as illustrated in FIG. 2, the SOC range (ofB2b (%) to B2c (%)) of the second energy storage device 6 usable forpower supply to the electric motor 3 is larger than the SOC range (partof the range less than or equal to Bib (%)) of the first energy storagedevice 5 usable for power supply to the electric motor 3.

Thus, in the CS mode, motive power that is supplementary to the motivepower of the internal combustion engine 2 to drive the drive wheel DW(propel the vehicle) can be generated quickly (with high responsivity)primarily by supplying power from the high-power second energy storagedevice 6 to the electric motor 3.

Accordingly, when the motive power system 1 outputs a high driving forceto the drive wheel DW, the electric motor 3 outputs auxiliary motivepower by power supply from the second energy storage device 6. Thisenables not only suppression of excessive fuel consumption of theinternal combustion engine 2 but also reduction in the displacement ofthe internal combustion engine 2.

In addition, since the second energy storage device 6 has a higher powerdensity than the first energy storage device 5, the resistance of thesecond energy storage device 6 to charge or discharge for which highresponsivity is required is superior to that of the first energy storagedevice 5. This can further suppress deterioration of the first energystorage device 5.

Main Routine Process

On the basis of the foregoing, a detailed description will be given ofthe control process for the control device 8. The control device 8sequentially executes a main routine process illustrated in a flowchartin FIG. 3 in a predetermined control process cycle when the vehicle isstarted.

In STEP1, the control device 8 acquires the current mode of the controlprocess, a detected value of the SOC of the first energy storage device5 (i.e., the first SOC), and a detected value of the SOC of the secondenergy storage device 6 (i.e., the second SOC).

If the first energy storage device 5 is charged up to the fully-chargedlevel (or up to the an SOC greater than or equal to a CS→CD switchingthreshold B1_mc2 described below) while the vehicle is at rest beforethe vehicle is started, the initial mode of the control process afterthe start of the vehicle is the CD mode. If the first energy storagedevice 5 is not charged while the vehicle is at rest before the vehicleis started, the initial mode of the control process after the start ofthe vehicle is the same mode as the mode set at the end of the previousdriving operation of the vehicle.

Then, in STEP2, the control device 8 determines whether or not thecurrent mode of the control process is the CD mode. If the determinationresult of STEP2 is affirmative, in STEP3, the control device 8 furtherdetermines whether or not the detected value of the first SOC is greaterthan or equal to a predetermined mode switching threshold B1_mc1. Themode switching threshold B1_mc1 is a threshold that defines whether ornot to perform switching from the CD mode to the CS mode, and ishereinafter referred to as the CD→CS switching threshold B1_mc1. In thisembodiment, the CD→CS switching threshold B1_mc1 is set to B1b (%)illustrated in FIG. 2.

If the determination result of STEP3 is affirmative, in STEP4, thecontrol device 8 selects the CD mode as the mode of the control processand executes a control process for the CD mode (described in detailbelow). In this case, the control process for the CD mode iscontinuously executed.

If the determination result of STEP3 is negative, then, in STEP5, thecontrol device 8 determines whether or not the detected value of thesecond SOC is greater than or equal to a mode switching thresholdB2_mc1. The mode switching threshold B2_mc1 is a threshold that defineswhether or not to perform switching from the first CS mode to the secondCS mode, and is hereinafter referred to as the CS1→CS2 switchingthreshold B2_mc1. In this embodiment, the CS1→CS2 switching thresholdB2_mc1 is set to B2c (%) illustrated in FIG. 2.

If the determination result of STEP5 is affirmative, in STEP6, thecontrol device 8 selects the first CS mode as the mode of the controlprocess and executes a control process for the first CS mode (describedin detail below). Thus, the mode of the control process is switched fromthe CD mode to the first CS mode.

If the determination result of STEP5 is negative, in STEP7, the controldevice 8 executes a power generation control process for performing apower generation operation of the electric generator 4.

In the power generation control process, the control device 8 instructsthe internal combustion engine operation controller 31 and the powertransmission controller 32 to perform a power generation operation ofthe electric generator 4.

In this case, the internal combustion engine operation controller 31controls the internal combustion engine 2 to output, from the internalcombustion engine 2, motive power to which motive power for driving theelectric generator 4 is added. The power transmission controller 32controls the power transmission circuit unit 7 to preferentially chargethe second energy storage device 6, out of the first energy storagedevice 5 and the second energy storage device 6, with generated powerproduced by the electric generator 4 which is supplied with the motivepower of the internal combustion engine 2. Specifically, the powertransmission controller 32 controls the voltage converter 24 and theinverter 22 of the power transmission circuit unit 7 to charge only thesecond energy storage device 6 with the generated power, except for thecase where the detected value of the first SOC is smaller than apredetermined value (e.g., a threshold B1_th1 described below (see FIG.11)).

If the detected value of the first SOC is smaller than the predeterminedvalue and while power supply to the electric motor 3 is halted, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 22 of the power transmission circuit unit 7 tocharge both the first energy storage device 5 and the second energystorage device 6 with the generated power. In this case, the amount ofgenerated power used to charge the first energy storage device 5 islimited to an amount of charging power at low rates (low speeds) tosuppress the progression of deterioration of the first energy storagedevice 5.

Thus, the second energy storage device 6 is preferentially charged withthe generated power. If the charge rate of the first energy storagedevice 5 is low, the first energy storage device 5 is appropriatelycharged with part of the generated power at a low rate.

Note that the internal combustion engine 2 is not always in operationand has not started its operation when the determination result of STEP5is negative. In this case, the control device 8 instructs the internalcombustion engine operation controller 31 and the power transmissioncontroller 32 to perform a power generation operation of the electricgenerator 4 after the internal combustion engine 2 has been started.

In the process for starting the internal combustion engine 2, the powertransmission circuit unit 7 controls the voltage converter 24 on thesecond energy storage device 6 side and the inverter 22 on the electricgenerator 4 side to supply power from the second energy storage device 6to the electric generator 4 (and to therefore cause the electricgenerator 4 to operate as a starter motor). This allows the output shaft2 a of the internal combustion engine 2 to be driven to rotate by themotive power of the electric generator 4 serving as a starter actuator(starter motor). In this embodiment, therefore, the second energystorage device 6 supplies power to the electric generator 4 (startermotor) when the internal combustion engine 2 is started.

Since instantaneous power supply to the starter actuator (the electricgenerator 4), which is required to start the internal combustion engine2, is undertaken by the second energy storage device 6, the progressionof deterioration of the first energy storage device 5 can be favorablysuppressed.

Then, the internal combustion engine operation controller 31 suppliesfuel to the internal combustion engine 2 in synchronization with therotation of the output shaft 2 a of the internal combustion engine 2 tostart the combustion operation of the internal combustion engine 2.Thereafter, the internal combustion engine operation controller 31 andthe power transmission controller 32 execute the control processdescribed above for performing a power generation operation of theelectric generator 4, thereby starting the power generation operation ofthe electric generator 4 and the charging of the second energy storagedevice 6 with the generated power.

After the power generation control process in STEP7, in STEP8, thecontrol device 8 selects the second CS mode as the mode of the controlprocess and executes a control process for the second CS mode (describedin detail below). Thus, the mode of the control process is switched fromthe CD mode to the second CS mode.

For additional explanation, in the second CS mode, the charging of thesecond energy storage device 6 through the power generation operation ofthe electric generator 4 is interrupted during the regenerativeoperation of the electric motor 3. In this case, the inverter 22 of thepower transmission circuit unit 7 is controlled so that the energizationof the inverter 22 is interrupted. Note that charging of the secondenergy storage device 6 with the regenerative power of the electricmotor 3 and charging of the second energy storage device 6 with thegenerated power of the electric generator 4 may be performed inparallel.

If the determination result of STEP2 is negative, then, in STEP9, thecontrol device 8 determines whether or not the current mode of thecontrol process is the first CS mode.

If the determination result of STEP9 is affirmative, in STEP10, thecontrol device 8 further determines whether or not the detected value ofthe first SOC is greater than or equal to a predetermined mode switchingthreshold B1_mc2. The mode switching threshold B1_mc2 is a thresholdthat defines whether or not to perform switching from the CS mode to theCD mode, and is hereinafter referred to as the CS→CD switching thresholdB1_mc2. In this embodiment, the CS→CD switching threshold B1_mc2 is setto a value higher than the mode switching threshold B1_mc1 in STEP3 toprovide hysteresis for switching between the first CS mode and thesecond CS mode, and is set to, for example, a value between B1b (%) andB1a (%) illustrated in FIG. 2.

If the determination result of STEP10 is affirmative, in STEP4, thecontrol device 8 selects the CD mode as the mode of the control processand executes the control process for the CD mode. Thus, the mode of thecontrol process is switched from the CS mode (first CS mode) to the CDmode.

If the determination result of STEP10 is negative, the control device 8executes the process from STEP5 described above. If the determinationresult of STEP5 is affirmative, the control process for the first CSmode is continuously executed. If the determination result of STEP5 isnegative, the mode of the control process is switched from the first CSmode to the second CS mode.

If the determination result of STEP9 is negative, in STEP11, the controldevice 8 further determines whether or not the detected value of thesecond SOC is greater than or equal to a predetermined mode switchingthreshold B2_mc2. The mode switching threshold B2_mc2 is a thresholdthat defines whether or not to perform switching from the second CS modeto the first CS mode, and is hereinafter referred to as the CS2→CS1switching threshold B2_mc2. In this embodiment, the CS2→CS1 switchingthreshold B2_mc2 is set to B2b (%) (>the CS1→CS2 switching thresholdB2_mc1) illustrated in FIG. 2.

If the determination result of STEP11 is affirmative, in STEP6, thecontrol device 8 selects the first CS mode as the mode of the controlprocess and executes the control process for the first CS mode. Thus,the mode of the control process is switched from the second CS mode tothe first CS mode.

If the determination result of STEP11 is negative, the control device 8executes the process from STEP7 described above. In this case, throughthe processing of STEP7 and STEP8, the power generation operation of theelectric generator 4 is continuously executed and the control process inthe second CS mode is also continuously executed.

As described above, switching between the CD mode and the CS mode isbased on the first SOC and switching between the first CS mode and thesecond CS mode is based on the second SOC.

Control Process for CD Mode

Next, the control process for the CD mode in STEP4 will be described indetail.

The control device 8 determines a required driving force (requiredpropulsion force) or required braking force of the entire vehicle inaccordance with the detected value of the amount of operation of theaccelerator pedal of the vehicle, the detected value of the amount ofoperation of the brake pedal of the vehicle, the detected value of thevehicle speed, and so on, and also determines the respective targetoperating states of the internal combustion engine 2, the electric motor3, the electric generator 4, the clutch 11, and the brake device.

In the CD mode, the control device 8 maintains the internal combustionengine 2 and the electric generator 4 at rest and also maintains theclutch 11 in the disconnected state.

In a situation where the required driving force of the entire vehicle isnot zero (this situation is hereinafter referred to as the vehicledriving request state), the control device 8 determines a requiredoutput DM_dmd of the electric motor 3 so as to realize the requireddriving force by using the motive power of the electric motor 3.

Then, as described in detail below, the control device 8 causes thepower transmission controller 32 to control the inverter 21 on theelectric motor 3 side and the voltage converters 23 and 24 of the powertransmission circuit unit 7 to supply power from either or both of thefirst energy storage device 5 and the second energy storage device 6 tothe electric motor 3 in accordance with a pre-created map illustrated inFIG. 4 on the basis of the required output DM_dmd and the detected valueof the SOC of the second energy storage device 6 (i.e., the second SOC).

Examples of the required output DM_dmd of the electric motor 3 mayinclude a request value of the amount of electrical energy to besupplied to the electric motor 3 per unit time (in other words, arequested power value), a driving force to be output from the electricmotor 3, and a request value of the amount of mechanical output energyper unit time, and a request value of the current which is to flowthrough the electric motor 3 to output motive power (an output torque)that can satisfy the required driving force of the vehicle from theelectric motor 3.

In this embodiment, the request value of the amount of electrical energyto be supplied to the electric motor 3 per unit time is used as anexample of the required output DM_dmd of the electric motor 3.

In a situation where the required braking force of the entire vehicle isnot zero (this situation is hereinafter referred to as the vehiclebraking request state), the control device 8 determines respectiveshares of the required braking force for the electric motor 3 and thebrake device. In this case, the control device 8 determines therespective shares for the electric motor 3 and the brake device on thebasis of the magnitude of the required braking force, the detected valueof the second SOC, and so on so as to basically maximize the share ofthe required braking force for the electric motor 3.

Then, the control device 8 causes the brake controller 34 to control thebrake device in accordance with the share of the required braking forcefor the brake device.

Further, the control device 8 determines a required amount ofregeneration G_dmd of the electric motor 3 so that the share of therequired braking force for the electric motor 3 is satisfied by aregenerative braking force generated through the regenerative operationof the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to chargeeither or both of the first energy storage device 5 and the secondenergy storage device 6 with the regenerative power output from theelectric motor 3 in accordance with a pre-created map illustrated inFIG. 9 on the basis of the required amount of regeneration G_dmd and thedetected value of the SOC of the second energy storage device 6 (i.e.,the second SOC). In this case, in this embodiment, the primary energystorage device to be charged with the regenerative power in the CD modeis the second energy storage device 6.

Examples of the required amount of regeneration G_dmd of the electricmotor 3 may include, as the share of the required braking force of theentire vehicle that is taken on by the electric motor 3, a request valueof the regenerative braking force generated by the electric motor 3performing a regenerative operation, a request value of the regenerativepower generated by the electric motor 3 performing a regenerativeoperation (the amount of electrical energy generated per unit time), anda request value of the current which is to flow through the electricmotor 3.

In this embodiment, the request value of the regenerative power is usedas an example of the required amount of regeneration G_dmd of theelectric motor 3.

Control Process During Power-Running Operation in CD Mode

A control process executed by the power transmission controller 32during the power-running operation of the electric motor 3 in the CDmode will be described in detail hereinafter with reference to FIGS. 4to 8.

FIG. 4 illustrates a map depicting how the output demand for the amountof electricity to be supplied (the amount of power supplied) to theelectric motor 3 is shared by the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required outputDM_dmd of the electric motor 3 and the second SOC.

In FIG. 4, diagonally hatched areas represent areas where all or part ofthe amount of power supplied to the electric motor 3 is taken on by thefirst energy storage device 5 and a shaded area represents an area whereall or part of the amount of power supplied to the electric motor 3 istaken on by the second energy storage device 6.

More specifically, the lower diagonally hatched area represents an areawhere all the amount of power supplied to the electric motor 3 is takenon only by the first energy storage device 5 and the shaded area or theupper diagonally hatched area represents an area where the amount ofpower supplied to the electric motor 3 is taken on by both the firstenergy storage device 5 and the second energy storage device 6.

On the map illustrated in FIG. 4, DM_max1 is a maximum value of therequired output DM_dmd in the CD mode. The maximum value DM_max1 is aconstant value when the second SOC is an SOC greater than or equal to apredetermined value B2e. When the second SOC is smaller than the valueB2e, the maximum value DM_max1 decreases in accordance with the decreasein the second SOC.

In the control process during the power-running operation of theelectric motor 3 in the CD mode, as illustrated in FIG. 4, the sharesfor the respective outputs of the first energy storage device 5 and thesecond energy storage device 6 are identified for the cases where thevalue of the second SOC falls within a high-SOC area(high-remaining-capacity area), a medium-SOC area(medium-remaining-capacity area), and a low-SOC area(low-remaining-capacity area) in the usable area of the second energystorage device 6 (the range of B2a to B2c illustrated in FIG. 2). Thehigh-SOC area is an area where SOC≧B2_th1 is satisfied. The medium-SOCarea is an area where B2_th1>SOC≧B2_th2 is satisfied. The low-SOC areais an area where B2_th2>SOC is satisfied.

On the map illustrated in FIG. 4, the thresholds B2_th1 and B2_th2 bywhich the second SOC is separated are thresholds (fixed values)determined in advance for the CD mode. The thresholds B2_th1 and B2_th2are set in advance experimentally, for example, so that the medium-SOCarea whose range is determined by the thresholds B2_th1 and B2_th2 is anSOC area within which the actual value of the second SOC preferablyfalls to minimize the progression of deterioration of the second energystorage device 6. Accordingly, the medium-SOC area is an area withinwhich the progression of deterioration of the second energy storagedevice 6 can be favorably suppressed when the second energy storagedevice 6 is charged or discharged with the actual value of the secondSOC being kept within the medium-SOC area as much as possible.

In this embodiment, the control process in the CD mode is performed withthe second SOC being kept within the medium-SOC as much as possible tosuppress the progression of deterioration of the second energy storagedevice 6.

In this embodiment, the threshold B2_th1, which is the lower limit ofthe high-SOC area, matches B2b (%) illustrated in FIG. 2. Accordingly,within the capacity of the second energy storage device 6, a capacity(stored energy) in the range of the high-SOC area is a dedicatedcapacity usable in the CD mode.

A control process for the power transmission controller 32 during thepower-running operation of the electric motor 3 in the CD mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 4 in accordance with a flowchart illustratedin FIGS. 5 to 7.

In STEP21, the power transmission controller 32 acquires the requiredoutput DM_dmd and a detected value of the second SOC. Then, in STEP22,the power transmission controller 32 determines whether or not thedetected value of the second SOC acquired in STEP21 is greater than orequal to the threshold B2_th1, which is the upper limit of themedium-SOC area.

The determination result of STEP22 is affirmative in the situation wherethe detected value of the second SOC falls within the high-SOC area. Inthis case, then, in STEP23, the power transmission controller 32determines whether or not the required output DM_dmd is less than orequal to a predetermined threshold DM_th1.

In this embodiment, the threshold DM_th1 is a threshold used for boththe medium-SOC area and the high-SOC area. As illustrated in FIG. 4, thethreshold DM_th1 is a predetermined constant value (fixed value) atvalues greater than or equal to a predetermined value B2d in themedium-SOC area. The constant value is a value determined so that theamount of power supplied corresponding to this value is sufficientlysmaller than the allowable upper limit on the amount of power suppliedto be output from the first energy storage device 5.

In a portion of the medium-SOC area smaller than the value B2d, thethreshold DM_th1 is set so that the amount of power suppliedcorresponding to the threshold DM_th1 matches a base amount of powersupplied P1_base described below (and consequently changes in accordancewith the second SOC). In this case, the threshold DM_th1 increases asthe second SOC decreases.

For additional explanation, the amount of power supplied correspondingto a certain threshold for the required output DM_dmd refers to theamount of electricity to be supplied to the electric motor 3 when therequired output DM_dmd matches this threshold.

The determination result of STEP23 is affirmative for the lowerdiagonally hatched area in the high-SOC area illustrated in FIG. 4. Inthis case, in STEP24, the power transmission controller 32 controls thevoltage converter 23 and the inverter 21 of the power transmissioncircuit unit 7 so that an output P1 of the first energy storage device 5matches the amount of power supplied corresponding to the requiredoutput DM_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block discharge from thesecond energy storage device 6.

The output P1 of the first energy storage device 5 is specifically anamount of electricity output (an amount of power discharged) from thefirst energy storage device 5, and an output P2 of the second energystorage device 6 (described below) is specifically an amount ofelectricity output (an amount of power discharged) from the secondenergy storage device 6. The amount of power supplied corresponding tothe required output DM_dmd refers to the amount of electricity to besupplied to the electric motor 3 to realize the required output DM_dmd.

If the determination result of STEP23 is negative, then, in STEP25, thepower transmission controller 32 determines whether or not the requiredoutput DM_dmd is less than or equal to a predetermined threshold DM_th2.

In this embodiment, similarly to the threshold DM_th1 in STEP23, thethreshold DM_th2 is a threshold used for both the medium-SOC area andthe high-SOC area. The threshold DM_th2 is set to a threshold largerthan the threshold DM_th1 by a predetermined amount.

In this case, the threshold DM_th2 may be set so that, for example, theamount of power supplied which is equivalent to the difference betweenthe threshold DM_th2 and the threshold DM_th1 (=DM_th2−DM_th1) is equalto the allowable upper limit on the amount of power supplied for thesecond energy storage device 6 in the CD mode or is equal to an amountof power supplied which is close to the allowable upper limit.

The determination result of STEP25 is affirmative for the shaded area inthe high-SOC area illustrated in FIG. 4. In this case, in STEP26, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 21 of the power transmission circuit unit 7 so thatthe output P1 of the first energy storage device 5 matches the amount ofpower supplied corresponding to the threshold DM_th1 and so that theoutput P2 of the second energy storage device 6 matches the amount ofpower supplied which is obtained by subtracting the output P1 of thefirst energy storage device 5 from the amount of power suppliedcorresponding to the required output DM_dmd.

On the other hand, the determination result of STEP25 is negative forthe upper diagonally hatched area in the high-SOC area illustrated inFIG. 4. In this situation, in STEP27, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the amount of power suppliedcorresponding to the difference between the thresholds DM_th1 and DM_th2(=DM_th2−DM_th1) and so that the output P1 of the first energy storagedevice 5 matches the amount of power supplied which is obtained bysubtracting the output P2 of the second energy storage device 6 from theamount of power supplied corresponding to the required output DM_dmd.

If the determination result of STEP22 is negative, then, in STEP28, thepower transmission controller 32 further determines whether or not thedetected value of the second SOC is greater than or equal to thethreshold B2th2, which is the lower limit of the medium-SOC area.

The determination result of STEP28 is affirmative in the situation wherethe detected value of the second SOC falls within the medium-SOC area.In this case, then, in STEP29 illustrated in FIG. 6, the powertransmission controller 32 determines the base amount of power suppliedP1_base, which is a base value of the output P1 of the first energystorage device 5, in accordance with the detected value of the secondSOC.

The base amount of power supplied P1_base is a lower limit on the amountof electricity that is output from the first energy storage device 5regardless of the required output DM_dmd of the electric motor 3 whenthe detected value of the second SOC falls within the medium-SOC area orthe low-SOC area. That is, in this embodiment, when the detected valueof the second SOC falls within the medium-SOC area or the low-SOC area,the power transmission circuit unit 7 is controlled so that the baseamount of power supplied P1_base or a larger amount of power supplied isoutput from the first energy storage device 5 regardless of the requiredoutput DM_dmd.

The base amount of power supplied P1_base is determined from thedetected value of the second SOC on the basis of a pre-created map or acalculation formula so that the base amount of power supplied P1_basechanges in accordance with the second SOC in a pattern indicated by abroken line illustrated in FIG. 4, for example. In this case, the baseamount of power supplied P1_base is determined to successively increasefrom zero to a maximum value P1b within the medium-SOC area inaccordance with the decrease in the second SOC and to be kept constantat the maximum value P1b within the low-SOC area. The maximum value P1bis a value larger than the amount of power supplied corresponding to thethreshold DM_th1 when the second SOC is greater than or equal to thepredetermined value B2d in the medium-SOC area.

After determining the base amount of power supplied P1_base in the waydescribed above, then, in STEP30, the power transmission controller 32determines whether or not the amount of power supplied corresponding tothe required output DM_dmd is smaller than the base amount of powersupplied P1_base.

The determination result of STEP30 is affirmative for an area below thebroken line within the lower diagonally hatched area in the medium-SOCarea illustrated in FIG. 4. In this situation, in STEP31, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theoutput P1 of the first energy storage device 5 matches the base amountof power supplied P1_base and so that an input Pc2 of the second energystorage device 6, that is, the amount of charging power, matches theamount of power supplied which is obtained by subtracting the amount ofpower supplied corresponding to the required output DM_dmd from the baseamount of power supplied P1_base.

If the determination result of STEP30 is negative, in STEP32, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to the threshold DM_th1.

The determination result of STEP32 is affirmative for an area obtainedby removing the area below the broken line from the lower diagonallyhatched area in the medium-SOC area illustrated in FIG. 4 (specifically,an area obtained by combining the area along the broken line and an areaabove the broken line).

In this situation, in STEP33, as in STEP24, the power transmissioncontroller 32 controls the voltage converter 23 and the inverter 21 ofthe power transmission circuit unit 7 so that the output P1 of the firstenergy storage device 5 matches the amount of power suppliedcorresponding to the required output DM_dmd. In this case, the voltageconverter 24 on the second energy storage device 6 side is controlled toblock discharge from the second energy storage device 6.

If the determination result of STEP32 is negative, in STEP34, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to the threshold DM_th2.

The determination result of STEP34 is affirmative for the shaded area inthe medium-SOC area illustrated in FIG. 4. In this situation, in STEP35,as in STEP26, the power transmission controller 32 controls the voltageconverters 23 and 24 and the inverter 21 of the power transmissioncircuit unit 7 so that the output P1 of the first energy storage device5 matches the amount of power supplied corresponding to the thresholdDM_th1 and so that the output P2 of the second energy storage device 6matches the amount of power supplied which is obtained by subtractingthe output P1 of the first energy storage device 5 from the amount ofpower supplied corresponding to the required output DM_dmd.

On the other hand, the determination result of STEP34 is negative forthe upper diagonally hatched area in the medium-SOC area illustrated inFIG. 4. In this situation, in STEP36, as in STEP27, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theoutput P2 of the second energy storage device 6 matches the amount ofpower supplied corresponding to the difference between the thresholdsDM_th1 and DM_th2 (=DM_th2−DM_th1) and so that the output P1 of thefirst energy storage device 5 matches the amount of power supplied whichis obtained by subtracting the output P2 of the second energy storagedevice 6 from the amount of power supplied corresponding to the requiredoutput DM_dmd.

Then, the determination result of STEP28 is negative in the situationwhere the detected value of the second SOC falls within the low-SOCarea. In this case, then, in STEP37 illustrated in FIG. 7, the powertransmission controller 32 determines the base amount of power suppliedP1_base by using the same or substantially the same process as that inSTEP29. Then, in STEP38, the power transmission controller 32 furtherdetermines whether or not the amount of power supplied corresponding tothe required output DM_dmd is smaller than the base amount of powersupplied P1_base.

The determination result of STEP38 is affirmative for an area below thebroken line within the lower diagonally hatched area in the low-SOC areaillustrated in FIG. 4. In this situation, in STEP39, as in STEP31, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 21 of the power transmission circuit unit 7 so thatthe output P1 of the first energy storage device 5 matches the baseamount of power supplied P1_base and so that the input Pc2 of the secondenergy storage device 6, that is, the amount of charging power, matchesthe amount of power supplied which is obtained by subtracting the amountof power supplied corresponding to the required output DM_dmd from thebase amount of power supplied P1_base.

If the determination result of STEP38 is negative, in STEP40, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to a predeterminedthreshold DM_th3.

The determination result of STEP40 is affirmative for an area obtainedby removing the area below the broken line from the diagonally hatchedarea in the low-SOC area illustrated in FIG. 4 (specifically, an areaobtained by combining the area along the broken line and an area abovethe broken line).

In this situation, in STEP41, as in STEP24 or STEP33, the powertransmission controller 32 controls the voltage converter 23 and theinverter 21 of the power transmission circuit unit 7 so that the outputP1 of the first energy storage device 5 matches the amount of powersupplied corresponding to the required output DM_dmd. In this case, thevoltage converter 24 on the second energy storage device 6 side iscontrolled to block discharge from the second energy storage device 6.

On the other hand, the determination result of STEP40 is negative forthe shaded area in the low-SOC area illustrated in FIG. 4. In thissituation, in STEP42, the power transmission controller 32 controls thevoltage converters 23 and 24 and the inverter 21 of the powertransmission circuit unit 7 so that the output P1 of the first energystorage device 5 matches the amount of power supplied corresponding tothe threshold DM_th3 and so that the output P2 of the second energystorage device 6 matches the amount of power supplied which is obtainedby subtracting the output P1 of the first energy storage device 5 fromthe amount of power supplied corresponding to the required outputDM_dmd.

The control process during the power-running operation of the electricmotor 3 in the CD mode is executed in the way described above. In thiscontrol process, when the detected value of the second SOC falls withinthe high-SOC area, power is supplied from the second energy storagedevice 6 to the electric motor 3 in a range where the required outputDM_dmd is less than or equal to the threshold DM_th2 (a comparativelycommonly used range), except for the case where the required outputDM_dmd is less than or equal to the comparatively small thresholdDM_th1. In the high-SOC area, furthermore, the second energy storagedevice 6 is not charged with power supplied by the first energy storagedevice 5.

This can make the second SOC close to the medium-SOC area where theprogression of deterioration of the second energy storage device 6 isfavorably suppressed.

When the detected value of the second SOC falls within the medium-SOCarea or the low-SOC area, if the amount of power supplied correspondingto the required output DM_dmd is less than or equal to the base amountof power supplied P1_base, the output P1 of the first energy storagedevice 5 is retained at the base amount of power supplied P1_base, whichis set in accordance with the detected value of the second SOC.

If the amount of power supplied corresponding to the required outputDM_dmd is smaller than the base amount of power supplied P1_base, theamount of power supplied corresponding to the required output DM_dmd,which is a portion of the base amount of power supplied P1_base, issupplied from only the first energy storage device 5 to the electricmotor 3 and, also, the second energy storage device 6 is charged withthe amount of power supplied which is obtained by subtracting the amountof power supplied corresponding to the required output DM_dmd from thebase amount of power supplied P1_base.

In addition, as the second SOC decreases, the range of the requiredoutput DM_dmd in which the second energy storage device 6 is chargedwith power supplied from the first energy storage device 5 is increasedand the amount of charging power of the second energy storage device 6is more likely to increase.

As a result, when the second SOC falls within the medium-SOC area or thelow-SOC area, if power is supplied from the second energy storage device6 to the electric motor 3, then, the second energy storage device 6 canbe basically replenished by being charged with power supplied from thefirst energy storage device 5, as appropriate. This enables the secondSOC to be maintained within the medium-SOC area as much as possible.Therefore, the progression of deterioration of the second energy storagedevice 6 can be minimized. In addition, a portion of the capacity of thesecond energy storage device 6 which is used in the CS mode, describedbelow, can be saved as much as possible.

Furthermore, when the second energy storage device 6 is charged, thebase amount of power supplied P1_base output from the first energystorage device 5 is set in accordance with the second SOC regardless ofthe required output DM_dmd. Thus, the output P2 or the input Pc2 of thesecond energy storage device 6 changes in response to a change in therequired output DM_dmd, and the change in the output P1 of the firstenergy storage device 5 is less sensitive to the change in the requiredoutput DM_dmd.

In particular, the base amount of power supplied P1_base in the low-SOCarea is a constant value (=P1b). This prevents the output P1 of thefirst energy storage device 5 from changing in accordance with thechange in required driving force DT_dmd.

As a result, in the situation where the second energy storage device 6is charged (when the amount of power supplied corresponding to therequired output DM_dmd is less than the base amount of power suppliedP1_base), the output P1 of the first energy storage device 5 is of highstability with less frequent changes. Therefore, the progression ofdeterioration of the first energy storage device 5 can be minimized.

In this embodiment, when the second SOC is greater than or equal to thepredetermined value B2d, if the amount of power supplied correspondingto the required output DM_dmd is less than or equal to the thresholdDM_th1, power is supplied from only the first energy storage device 5 tothe electric motor 3. This can reduce the load on the second energystorage device 6 when the second SOC is greater than or equal to thepredetermined value B2d, resulting in the total amount of heatgeneration of the first energy storage device 5 and the second energystorage device 6 being reduced.

FIG. 8 is a graph illustrating how the respective amounts of heatgeneration of the energy storage devices 5 and 6 and the total amount ofheat generation of the energy storage devices 5 and 6 change in responseto a change in percentage shares X1 and X2 of the constant requiredoutput DM_dmd for the first energy storage device 5 and the secondenergy storage device 6.

The percentage share X1 refers to the proportion of a share of theamount of power supplied corresponding to the constant required outputDM_dmd that is taken on by the first energy storage device 5, and thepercentage share X2 refers to the proportion of a share of the amount ofpower supplied corresponding to the constant required output DM_dmd thatis taken on by the second energy storage device 6.

The second energy storage device 6 with relatively high power densityhas a lower impedance (internal resistance) than the first energystorage device 5 with relatively high energy density but includes fewercells connected in parallel than the first energy storage device 5, andtherefore has a lower output voltage than the first energy storagedevice 5. For this reason, when the percentage share X2 for the secondenergy storage device 6 is increased with respect to a certain constantvalue of the required output DM_dmd, the amount of heat generation ofthe second energy storage device 6 is more likely to increase than whenthe percentage share X1 for the first energy storage device 5 isincreased (see two thin lines in the graph illustrated in FIG. 8).

As a result, as indicated by a thick line in the graph illustrated inFIG. 8, the total amount of heat generation of the first energy storagedevice 5 and the second energy storage device 6 becomes minimum when thepercentage share X1 is greater than the percentage share X2.

In this embodiment, accordingly, when the second SOC is greater than orequal to the predetermined value B2d, if the amount of power suppliedcorresponding to the required output DM_dmd is less than or equal to thethreshold DM_th1, power is supplied from only the first energy storagedevice 5 to the electric motor 3 to reduce the load on the second energystorage device 6 to such an extent that the load placed on the firstenergy storage device 5 does not become excessive.

This configuration can minimize the total amount of heat generation ofthe first energy storage device 5 and the second energy storage device 6while preventing the second energy storage device 6 from generatingexcessive heat. In other words, the demand can be prevented from beingconcentrated in one of the first energy storage device 5 and the secondenergy storage device 6.

Control Process During Regenerative Operation in CD Mode

Next, a control process executed by the power transmission controller 32during the regenerative operation of the electric motor 3 in the CD modewill be described in detail hereinafter with reference to FIGS. 9 and10.

FIG. 9 is a map that defines how the regenerative power output by theelectric motor 3 during the regenerative operation in the CD mode isshared in order to charge the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required amount ofregeneration G_dmd of the electric motor 3 and the second SOC.

In FIG. 9, diagonally hatched areas represent areas where all or part ofthe regenerative power generated by the electric motor 3 is used tocharge the first energy storage device 5, and a shaded area representsan area where all or part of the regenerative power is used to chargethe second energy storage device 6.

More specifically, the lower diagonally hatched area in the medium-SOCarea and the high-SOC area of the second SOC represents an area whereall of the regenerative power is used to charge only the first energystorage device 5. The shaded area in the medium-SOC area and thehigh-SOC area of the second SOC and the upper diagonally hatched area inthe low-SOC area and the medium-SOC area represent areas where theregenerative power is used to charge both the first energy storagedevice 5 and the second energy storage device 6. The shaded area in thelow-SOC area of the second SOC represents an area where all of theregenerative power is used to charge only the second energy storagedevice 6.

On the map illustrated in FIG. 9, G_max1 is a maximum value of therequired amount of regeneration G_dmd in the CD mode. The maximum valueG_max1 is a constant value when the second SOC is an SOC less than orequal to a predetermined value B2f in the high-SOC area. When the secondSOC is larger than the value B2f, the maximum value G_max1 decreases asthe second SOC increases.

The control process for the power transmission controller 32 during theregenerative operation of the electric motor 3 in the CD mode issequentially executed in a predetermined control process cycle inaccordance with a flowchart illustrated in FIG. 10 by using the mapillustrated in FIG. 9.

In STEP51, the power transmission controller 32 acquires the requiredamount of regeneration G_dmd and a detected value of the second SOC.

Then, in STEP52, the power transmission controller 32 determines whetheror not the required amount of regeneration G_dmd is less than or equalto a predetermined threshold G_th1.

In this embodiment, the threshold G_th1 is set in accordance with thesecond SOC. Specifically, as illustrated in the example in FIG. 9, whenthe second SOC falls within the high-SOC area, the threshold G_th1 isset to a predetermined constant value.

When the second SOC falls within the medium-SOC area, the thresholdG_th1 is set to successively decrease from the constant value to zero inaccordance with the decrease in the second SOC. In the low-SOC area ofthe second SOC, the threshold G_th1 is set to zero.

The amount of charging power corresponding to a maximum value of thethreshold G_th1 (the constant value in the high-SOC area) is an upperlimit on the amount of regenerative power used to charge the firstenergy storage device 5. The upper limit is determined to be acomparatively small value so as to allow the first energy storage device5 to be charged at a low rate (low speed) to minimize the progression ofdeterioration of the first energy storage device 5.

For additional explanation, the amount of charging power correspondingto a certain threshold for the required amount of regeneration G_dmdrefers to the amount of electricity representing the total regenerativepower output from the electric motor 3 when the required amount ofregeneration G_dmd matches this threshold.

The determination result of STEP52 is affirmative for the lowerdiagonally hatched area illustrated in FIG. 9. In this situation, inSTEP53, the power transmission controller 32 controls the voltageconverter 23 and the inverter 21 of the power transmission circuit unit7 so that an input Pc1 of the first energy storage device 5 matches theamount of charging power corresponding to the required amount ofregeneration G_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block charging of thesecond energy storage device 6.

The input Pc1 of the first energy storage device 5 is specifically anamount of electricity used to charge the first energy storage device 5(the amount of charging power), and the input Pc2 of the second energystorage device 6 (described below) is specifically an amount ofelectricity used to charge the second energy storage device 6 (an amountof charging power). The amount of charging power corresponding to therequired amount of regeneration G_dmd refers to the amount ofelectricity representing the regenerative power output from the electricmotor 3 when the regenerative operation of the electric motor 3 isperformed in accordance with the required amount of regeneration G_dmd.

For additional explanation, when the detected value of the second SOCduring the regenerative operation of the electric motor 3 falls withinthe low-SOC area, the threshold G_th1 is zero and thus no affirmativedetermination is made in STEP52. Thus, in this case, the processing ofSTEP53 is not executed.

If the determination result of STEP52 is negative, then, in STEP54, thepower transmission controller 32 determines whether or not the requiredamount of regeneration G_dmd is less than or equal to a predeterminedthreshold G_th2.

In this embodiment, the threshold G_th2 is set in accordance with thesecond SOC in a way similar to that for the threshold G_th1 in STEP52described above. Specifically, as illustrated in the example in FIG. 9,when the second SOC falls within the low-SOC area, the threshold G_th2is set to a predetermined constant value. The constant value is set sothat the amount of charging power corresponding to the differencebetween the threshold G_th2 and the maximum value G_max1 of the requiredamount of regeneration G_dmd (=G_max1−G_th2) matches the amount ofcharging power corresponding to the maximum value of the threshold G_th1(the value of the threshold G_th1 in the high-SOC area), that is, theupper limit on the amount of charging power of the first energy storagedevice 5.

When the second SOC falls within the medium-SOC area, the thresholdG_th2 is set to increase to the maximum value G_max1 in accordance withthe increase in the second SOC in a pattern similar to the pattern inwhich the threshold G_th1 changes. In the high-SOC area of the secondSOC, the threshold G_th1 is kept at the constant maximum value G_max1.

In the medium-SOC area, the thresholds G_th1 and G_th2 are set so thatthe sum of the amount of charging power corresponding to the differencebetween the maximum value G_max1 and the threshold G_th2 (=G_max1−G_th2)and the amount of charging power corresponding to the threshold G_th1matches the upper limit on the amount of charging power of the firstenergy storage device 5.

The determination result of STEP54 is affirmative for the shaded areaillustrated in FIG. 9. In this situation, in STEP55, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc1 of the first energy storage device 5 matches the amount ofcharging power corresponding to the threshold G_th1 and so that theinput Pc2 of the second energy storage device 6 matches the amount ofcharging power obtained by subtracting the input Pc1 of the first energystorage device 5 from the amount of charging power corresponding to therequired amount of regeneration G_dmd.

On the other hand, the determination result of STEP54 is negative forthe upper diagonally hatched area in the low-SOC area or the medium-SOCarea illustrated in FIG. 9. In this situation, in STEP56, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc2 of the second energy storage device 6 matches the amount ofcharging power corresponding to the difference between the thresholdsG_th1 and G_th2 (=G_th2−G_th1) and so that the input Pc1 of the firstenergy storage device 5 matches the amount of charging power obtained bysubtracting the input Pc2 of the second energy storage device 6 from theamount of charging power corresponding to the required amount ofregeneration G_dmd.

For additional explanation, when the detected value of the second SOCduring the regenerative operation of the electric motor 3 falls withinthe high-SOC area, the threshold G_th2 matches the maximum value G_max1and thus no negative determination is made in STEP54. Thus, in thiscase, the processing of STEP56 is not executed.

The control process during the regenerative operation of the electricmotor 3 in the CD mode is executed in the way described above. In thiscontrol process, when the detected value of the second SOC is largerthan the threshold B2_th2, which is the lower limit of the medium-SOCarea, the first energy storage device 5 is preferentially charged withregenerative power in the range where the required amount ofregeneration G_dmd is less than or equal to the threshold G_th1.

Further, when the detected value of the second SOC is smaller than thethreshold B2_th1, which is the upper limit of the medium-SOC area, thefirst energy storage device 5 is charged with regenerative power withina range where the required amount of regeneration G_dmd is larger thanthe threshold G_th2.

The amount of regenerative power used to charge the first energy storagedevice 5 is limited to a value less than or equal to a predeterminedupper limit (the amount of charging power corresponding to the thresholdG_th1 in the high-SOC area).

This configuration enables the first energy storage device 5 to becharged with regenerative power at a low rate. This can restore the SOCof the first energy storage device 5 while suppressing the progressionof deterioration of the first energy storage device 5.

When the detected value of the second SOC is smaller than the thresholdB2_th2, which is the lower limit of the medium-SOC area, the secondenergy storage device 6 is preferentially charged with regenerativepower. When the detected value of the second SOC is larger than thethreshold B2_th2, which is the lower limit of the medium-SOC area, thesecond energy storage device 6 is charged with regenerative power withina range where the required amount of regeneration G_dmd is larger thanthe threshold G_th1.

This configuration enables the second energy storage device 6 to becharged with regenerative power so that the SOC of the second energystorage device 6 can be kept within the medium-SOC area as much aspossible. As a result, the progression of deterioration of the secondenergy storage device 6 can be minimized, and a portion of the capacityof the second energy storage device 6 which is used in the CS mode,described below, can be saved as much as possible.

Control Process for First CS Mode

Next, the control process for the first CS mode in STEP6 will bedescribed in detail with reference to FIGS. 11 to 15.

The control device 8 determines a required driving force (requiredpropulsion force) or required braking force of the entire vehicle in away similar to that in the CD mode and also determines the respectivetarget operating states of the internal combustion engine 2, theelectric motor 3, the electric generator 4, the clutch 11, and the brakedevice.

In the first CS mode, the control device 8 determines the necessity ofoperation of the internal combustion engine 2 and the necessity of powergeneration operation of the electric generator 4, if necessary, inaccordance with the required driving force or required braking force ofthe entire vehicle, the detected value of the second SOC, or the like,and controls the operation of the internal combustion engine 2 and theelectric generator 4 in accordance with the determination result.

In this case, the start of the internal combustion engine 2 and thepower generation operation of the electric generator 4 are performed inthe way described above in connection with the processing of STEP7.

In the vehicle driving request state (in the state where the requireddriving force is not zero) during the operation of the internalcombustion engine 2, the control device 8 determines the respectiveshares of the required driving force of the entire vehicle that aretaken on by the electric motor 3 and the internal combustion engine 2 inaccordance with the required driving force of the entire vehicle, thedetected values of the first SOC and the second SOC, and so on.

In this case, the respective shares for the electric motor 3 and theinternal combustion engine 2 are determined so that, basically, exceptfor the case where the second SOC is comparatively high, all or a largeportion of the required driving force is taken on by the internalcombustion engine 2 and the electric motor 3 serves in an auxiliaryrole.

The control device 8 causes the internal combustion engine operationcontroller 31 to control the motive power (output torque) of theinternal combustion engine 2 in accordance with the share of therequired driving force for the internal combustion engine 2, and alsocauses the clutch controller 33 to control the operating state of theclutch 11. In a situation where the power generation operation of theelectric generator 4 is performed, motive power necessary for the powergeneration operation of the electric generator 4 is added to the motivepower of the internal combustion engine 2.

Further, the control device 8 determines the required output DM_dmd ofthe electric motor 3 so that the share of the required driving force forthe electric motor 3 is satisfied by the motive power generated throughthe power-running operation of the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to supplypower from either or both of the first energy storage device 5 and thesecond energy storage device 6 to the electric motor 3 in accordancewith a pre-created map illustrated in FIG. 11 on the basis of therequired output DM_dmd and the detected value of the SOC of the firstenergy storage device 5 (i.e., the first SOC).

In the first CS mode, even in a situation where the share of therequired driving force for the electric motor 3 is zero (a situationwhere the power-running operation of the electric motor 3 is notperformed), the control device 8 causes the power transmissioncontroller 32 to control the voltage converters 23 and 24 of the powertransmission circuit unit 7 so that, when the detected value of thefirst SOC is comparatively small, the first energy storage device 5 ischarged with power supplied from the second energy storage device 6.

In the vehicle driving request state when the internal combustion engine2 is not in operation, the control device 8 determines the requiredoutput DM_dmd of the electric motor 3 so that the required driving forceof the entire vehicle is satisfied by the motive power generated throughthe power-running operation of the electric motor 3.

Then, similarly to when the internal combustion engine 2 is inoperation, the control device 8 causes the power transmission controller32 to control the inverter 21 on the electric motor 3 side and thevoltage converters 23 and 24 of the power transmission circuit unit 7 inaccordance with the map illustrated in FIG. 11 on the basis of therequired output DM_dmd and the detected value of the first SOC.

In the vehicle braking request state (in the state where the requiredbraking force is not zero), the control device 8 determines therespective shares of the required braking force of the entire vehiclefor the electric motor 3 and the brake device. In this case, the controldevice 8 determines the respective shares for the electric motor 3 andthe brake device on the basis of the magnitude of the required brakingforce, the detected value of the first SOC, and so on so as to basicallymaximize the share of the required braking force for the electric motor3.

Then, the control device 8 causes the brake controller 34 to control thebrake device in accordance with the share of the required braking forcefor the brake device.

Further, the control device 8 determines the required amount ofregeneration G_dmd of the electric motor 3 so that the share of therequired braking force for the electric motor 3 is satisfied by theregenerative braking force generated through the regenerative operationof the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to chargeeither or both of the first energy storage device 5 and the secondenergy storage device 6 with the regenerative power output from theelectric motor 3 in accordance with a pre-created map illustrated inFIG. 14 on the basis of the required amount of regeneration G_dmd andthe detected value of the second SOC. In this embodiment, the primaryenergy storage device to be charged with the regenerative power in thefirst CS mode is the second energy storage device 6.

The power generation operation of the electric generator 4 is stoppedduring the regenerative operation of the electric motor 3 or duringpower supply from the second energy storage device 6 to the electricmotor 3. Note that charging of the second energy storage device 6 withthe regenerative power of the electric motor 3 and charging of thesecond energy storage device 6 with the generated power of the electricgenerator 4 may be performed in parallel.

Control Process During Power-Running Operation in First CS Mode

A control process executed by the power transmission controller 32during the power-running operation of the electric motor 3 in the firstCS mode will be described in detail hereinafter with reference to FIGS.11 to 13.

FIG. 11 illustrates a map depicting how the output demand for the amountof electricity to be supplied (the amount of power supplied) to theelectric motor 3 is shared by the first energy storage device 5 and thesecond energy storage device 6 in the first CS mode in accordance withthe required output DM_dmd of the electric motor 3 and the first SOC.

In FIG. 11, diagonally hatched areas represent areas where all or partof the amount of power supplied to the electric motor 3 is taken on bythe first energy storage device 5, and a shaded area represents an areawhere all or part of the amount of power supplied to the electric motor3 is taken on by the second energy storage device 6.

More specifically, the lower diagonally hatched area represents an areawhere all the amount of power supplied to the electric motor 3 is takenon only by the first energy storage device 5, and a shaded arearepresents an area where the amount of power supplied to the electricmotor 3 is taken on only by the second energy storage device 6 or theamount of power supplied to the electric motor 3 is taken on by both thefirst energy storage device 5 and the second energy storage device 6.The upper diagonally hatched area represents an area where the amount ofpower supplied to the electric motor 3 is taken on by both the firstenergy storage device 5 and the second energy storage device 6.

On the map illustrated in FIG. 11, DM_max2 is a maximum value of therequired output DM_dmd in the first CS mode. The maximum value DM_max2is a constant value.

In the control process during the power-running operation of theelectric motor 3 in the first CS mode, as illustrated in FIG. 11, theshares for the respective outputs of the first energy storage device 5and the second energy storage device 6 are identified for the caseswhere the value of the first SOC falls within a high-SOC area(high-remaining-capacity area) and a low-SOC area(low-remaining-capacity area) in the range between the CD→CS switchingthreshold B1_mc1 (see FIG. 2) and the CS→CD switching threshold B1_mc2(see FIG. 2) described above. The high-SOC area is an area whereSOC≧B1_th1 is satisfied, and the low-SOC area is an area whereSOC<B1_th1 is satisfied. B1_th1 is a predetermined threshold (fixedvalue) between the CD-+CS switching threshold B1_mc1 and the CS→CDswitching threshold B1_mc2.

The control process for the power transmission controller 32 during thepower-running operation of the electric motor 3 in the first CS mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 11 in accordance with a flowchartillustrated in FIGS. 12 and 13.

In STEP61, the power transmission controller 32 acquires the requiredoutput DM_dmd and a detected value of the first SOC. Then, in STEP62,the power transmission controller 32 determines whether or not thedetected value of the first SOC acquired in STEP61 is greater than orequal to the threshold B1_th1.

The determination result of STEP62 is affirmative in the situation wherethe detected value of the first SOC falls within the high-SOC area. Inthis case, then, in STEP63, the power transmission controller 32determines whether or not the required output DM_dmd is less than orequal to a predetermined threshold DM_th5.

As illustrated in FIG. 11, the threshold DM_th5 is a predeterminedconstant value (fixed value) when the first SOC is a value greater thanor equal to a predetermined value B1c that is slightly larger than thethreshold B1_th1. The constant value is a value sufficiently smallerthan the allowable upper limit on the amount of power supplied to beoutput from the first energy storage device 5.

In the area less than the value B1c (the range of B1c to B1_th1), thethreshold DM_th5 is set to decrease to zero in accordance with thedecrease in the first SOC.

The determination result of STEP63 is affirmative for the lowerdiagonally hatched area in the high-SOC area illustrated in FIG. 11. Inthis case, in STEP64, the power transmission controller 32 controls thevoltage converter 23 and the inverter 21 of the power transmissioncircuit unit 7 so that the output P1 of the first energy storage device5 matches the amount of power supplied corresponding to the requiredoutput DM_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block discharge from thesecond energy storage device 6.

If the determination result of STEP63 is negative, then, in STEP65, thepower transmission controller 32 determines whether or not the requiredoutput DM_dmd is less than or equal to a predetermined threshold DM_th6.

In this embodiment, the threshold DM_th6 is a threshold used for boththe high-SOC area and the low-SOC area of the second SOC. The thresholdDM_th6 is set to a threshold that is larger than the threshold DM_th5 bya predetermined amount in the high-SOC area, and is set to a thresholdthat is larger than zero by the predetermined amount (i.e., thethreshold is equal to the predetermined amount) in the low-SOC area.

In this case, the threshold DM_th6 can be set so that, for example, theamount of power supplied corresponding to the predetermined amount isequal to the allowable upper limit on the amount of power supplied forthe second energy storage device 6 in the first CS mode or an amount ofpower supplied which is close to the allowable upper limit.

The required output DM_dmd, which is less than or equal to the thresholdDM_th6, is in a commonly used range of the electric motor 3 in the firstCS mode.

The determination result of STEP65 is affirmative for the shaded area inthe high-SOC area illustrated in FIG. 11. In this case, in STEP66, thepower transmission controller 32 controls the voltage converters 23 and24 and the inverter 21 of the power transmission circuit unit 7 so thatthe output P1 of the first energy storage device 5 matches the amount ofpower supplied corresponding to the threshold DM_th5 and so that theoutput P2 of the second energy storage device 6 matches the amount ofpower supplied which is obtained by subtracting the output P1 of thefirst energy storage device 5 from the amount of power suppliedcorresponding to the required output DM_dmd.

On the other hand, the determination result of STEP65 is negative forthe upper diagonally hatched area in the high-SOC area illustrated inFIG. 11. In this situation, in STEP67, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the amount of power suppliedcorresponding to the difference between the thresholds DM_th5 and DM_th6(=DM_th6−DM_th5) and so that the output P1 of the first energy storagedevice 5 matches the amount of power supplied which is obtained bysubtracting the output P2 of the second energy storage device 6 from theamount of power supplied corresponding to the required output DM_dmd.

The determination result of STEP62 is negative in the situation wherethe detected value of the first SOC falls within the low-SOC area. Inthis case, in STEP68 illustrated in FIG. 13, the power transmissioncontroller 32 further determines a base amount of power suppliedP2_base, which is a base value of the output P2 of the second energystorage device 6, in accordance with the detected value of the firstSOC.

The base amount of power supplied P2_base is a lower limit on the amountof electricity that is output from the second energy storage device 6regardless of the required output DM_dmd of the electric motor 3 whenthe detected value of the first SOC falls within the low-SOC area. Thatis, in this embodiment, when the detected value of the first SOC fallswithin the low-SOC area during the power-running operation of theelectric motor 3, the power transmission circuit unit 7 is controlled sothat the base amount of power supplied P2_base or a larger amount ofpower supplied is output from the second energy storage device 6regardless of the required output DM_dmd.

In this embodiment, in the first CS mode, the power transmission circuitunit 7 is controlled so that also in a situation where the power-runningoperation of the electric motor 3 is not performed (in a situation wherethe required driving force of the entire vehicle is taken on only by theinternal combustion engine 2), the base amount of power supplied P2_baseis output from the second energy storage device 6 to charge the firstenergy storage device 5.

The base amount of power supplied P2_base is determined from thedetected value of the first SOC on the basis of a pre-created map or acalculation formula so that the base amount of power supplied P2_basechanges in accordance with the first SOC in a pattern indicated by abroken line illustrated in FIG. 11, for example. In this case, the baseamount of power supplied P2_base is determined to successively increasefrom zero to a maximum value P2b in accordance with the decrease in thefirst SOC when the first SOC is an SOC in a range between the thresholdB1_th1 and a predetermined value Bid that is slightly smaller than thethreshold B1_th1, and is determined to be kept constant at the maximumvalue P2b in an area where the first SOC is less than or equal to thepredetermined value Bid. The maximum value P2b is a value smaller thanthe amount of power supplied corresponding to the threshold DM_th6 forthe required output DM_dmd in the low-SOC area of the first SOC. Themaximum value P2b is set so that, even if a large portion of the maximumvalue P2b is used to charge the first energy storage device 5, the firstenergy storage device 5 can be charged at a low rate at which theprogression of deterioration of the first energy storage device 5 can besuppressed.

After determining the base amount of power supplied P2_base in the waydescribed above, then, in STEP69, the power transmission controller 32determines whether or not the amount of power supplied corresponding tothe required output DM_dmd is smaller than the base amount of powersupplied P2_base.

The determination result of STEP69 is affirmative for an area below thebroken line within the shaded area in the low-SOC area illustrated inFIG. 11. In this situation, in STEP70, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the base amount of power suppliedP2_base and so that the input Pc1 (the amount of charging power) of thefirst energy storage device 5 matches the amount of power supplied whichis obtained by subtracting the amount of power supplied corresponding tothe required output DM_dmd from the base amount of power suppliedP2_base.

If the determination result of STEP69 is negative, in STEP71, the powertransmission controller 32 further determines whether or not therequired output DM_dmd is less than or equal to the threshold DM_th6.

The determination result of STEP71 is affirmative for an area obtainedby removing the area below the broken line from the shaded area in thelow-SOC area illustrated in FIG. 11 (specifically, an area obtained bycombining the area along the broken line and an area above the brokenline).

In this situation, in STEP72, the power transmission controller 32controls the voltage converter 24 and the inverter 21 of the powertransmission circuit unit 7 so that the output P2 of the second energystorage device 6 matches the amount of power supplied corresponding tothe required output DM_dmd. In this case, the voltage converter 23 onthe first energy storage device 5 side is controlled to block dischargefrom the first energy storage device 5.

On the other hand, the determination result of STEP71 is negative forthe upper diagonally hatched area in the low-SOC area illustrated inFIG. 11. In this situation, in STEP73, the power transmission controller32 controls the voltage converters 23 and 24 and the inverter 21 of thepower transmission circuit unit 7 so that the output P2 of the secondenergy storage device 6 matches the amount of power suppliedcorresponding to the threshold DM_th6 in the low-SOC area and so thatthe output P1 of the first energy storage device 5 matches the amount ofpower supplied which is obtained by subtracting the output P2 of thesecond energy storage device 6 from the amount of power suppliedcorresponding to the required output DM_dmd.

The control process during the power-running operation of the electricmotor 3 in the first CS mode is executed in the way described above. Inthis control process, when the detected value of the first SOC fallswithin the low-SOC area, the output P2 of the second energy storagedevice 6 is retained at the base amount of power supplied P2_base, whichis set in accordance with the detected value of the first SOC, if theamount of power supplied corresponding to the required output DM_dmd isless than or equal to the base amount of power supplied P2_base.

If the amount of power supplied corresponding to the required outputDM_dmd is larger than the base amount of power supplied P2_base, theamount of power supplied corresponding to the required output DM_dmd,which is a portion of the base amount of power supplied P2_base, issupplied from only the second energy storage device 6 to the electricmotor 3 and, also, the first energy storage device 5 is charged with theamount of power supplied which is obtained by subtracting the amount ofpower supplied corresponding to the required output DM_dmd from the baseamount of power supplied P2_base. This can gradually restore the firstSOC.

In this case, furthermore, high-accuracy adjustment of the rate ofcharging of the first energy storage device 5 is achievable by the powertransmission controller 32 controlling the voltage converters 23 and 24.Accordingly, the first energy storage device 5 is charged at a low rate,resulting in the progression of deterioration of the first energystorage device 5 being more effectively suppressed than when the firstenergy storage device 5 is charged with the generated power output bythe electric generator 4 by using the motive power of the internalcombustion engine 2.

When the detected value of the first SOC falls within the high-SOC area,power is supplied preferentially from the first energy storage device 5to the electric motor 3 if the required output DM_dmd is less than orequal to the threshold DM_th5.

This configuration can reduce the load on the second energy storagedevice 6 in the first CS mode, and prevent the second energy storagedevice 6 from generating excessive heat.

Control Process During Regenerative Operation in First CS Mode

Next, a control process executed by the power transmission controller 32during the regenerative operation of the electric motor 3 in the firstCS mode will be described in detail hereinafter with reference to FIGS.14 and 15.

FIG. 14 is a map that defines how the regenerative power output by theelectric motor 3 during the regenerative operation in the first CS modeis shared in order to charge the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required amount ofregeneration G_dmd of the electric motor 3 and the first SOC (the firstSOC in the range between the CD→CS switching threshold B1_mc1 and theCS→CD switching threshold B1_mc2).

In FIG. 14, a diagonally hatched area represents an area where all orpart of the regenerative power generated by the electric motor 3 is usedto charge the first energy storage device 5, and a shaded arearepresents an area where all or part of the regenerative power is usedto charge the second energy storage device 6.

On the map illustrated in FIG. 14, G_max2 is a maximum value of therequired amount of regeneration G_dmd in the first CS mode. The maximumvalue G_max2 is a constant value when the first SOC is an SOC less thanor equal to a predetermined value B1e that is slightly smaller than theCS→CD switching threshold B1_mc2. When the first SOC is larger than thevalue B1e, the maximum value G_max2 decreases in accordance with theincrease in the first SOC.

A control process for the power transmission controller 32 during theregenerative operation of the electric motor 3 in the first CS mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 14 in accordance with a flowchartillustrated in FIG. 15.

In STEP81, the power transmission controller 32 acquires the requiredamount of regeneration G_dmd and a detected value of the first SOC.

Then, in STEP82, the power transmission controller 32 determines whetheror not the required amount of regeneration G_dmd is less than or equalto a predetermined threshold G_th4.

In this embodiment, the threshold G_th4 is set in accordance with thefirst SOC. Specifically, as illustrated in the example in FIG. 14, thethreshold G_th4 is set to a predetermined constant value when the firstSOC is an SOC less than or equal to the predetermined value B1e. Theconstant value is determined to be a comparatively small value so as toallow the first energy storage device 5 to be charged at a low rate (lowspeed) to minimize the progression of deterioration of the first energystorage device 5.

When the first SOC is larger than the predetermined value B1e, thethreshold G_th4 is set to successively decrease from the constant valueto zero (reach zero at the CS→CD switching threshold B1_mc2) inaccordance with the decrease in the first SOC.

The determination result of STEP82 is affirmative for the diagonallyhatched area illustrated in FIG. 14. In this situation, in STEP83, thepower transmission controller 32 controls the voltage converter 23 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc1 of the first energy storage device 5 matches the amount ofcharging power corresponding to the required amount of regenerationG_dmd. In this case, the voltage converter 24 on the second energystorage device 6 side is controlled to block charging of the secondenergy storage device 6.

On the other hand, the determination result of STEP82 is negative forthe shaded area illustrated in FIG. 14. In this situation, in STEP84,the power transmission controller 32 controls the voltage converters 23and 24 and the inverter 21 of the power transmission circuit unit 7 sothat the input Pc1 of the first energy storage device 5 matches theamount of charging power corresponding to the threshold G_th4 and sothat the input Pc2 of the second energy storage device 6 matches theamount of charging power obtained by subtracting the input Pc1 of thefirst energy storage device 5 from the amount of charging powercorresponding to the required amount of regeneration G_dmd.

The control process during the regenerative operation of the electricmotor 3 in the first CS mode is executed in the way described above.This control process allows the first energy storage device 5 to bepreferentially charged with regenerative power if the required amount ofregeneration G_dmd is less than or equal to the threshold G_th4. Inaddition, the amount of charging power of the first energy storagedevice 5 is limited to a value less than or equal to the amount ofcharging power corresponding to the threshold G_th4. This can restorethe first SOC while minimizing the progression of deterioration of thefirst energy storage device 5.

Control Process for Second CS Mode

Next, the control process for the second CS mode in STEP8 will bedescribed in detail with reference to FIGS. 16 to 20.

The control device 8 determines a required driving force (requiredpropulsion force) or required braking force of the entire vehicle in away similar to that in the CD mode, and also determines the respectivetarget operating states of the internal combustion engine 2, theelectric motor 3, the electric generator 4, the clutch 11, and the brakedevice.

In the second CS mode, the control device 8 causes the internalcombustion engine operation controller 31 to control the internalcombustion engine 2 to successively perform the operation of theinternal combustion engine 2. In addition to this, the control device 8causes the power transmission controller 32 to control the electricgenerator 4 to continuously perform the power generation operation ofthe electric generator 4, except during the rotation operation of theelectric motor 3. In this case, the power transmission controller 32controls the voltage converter 24 and the inverter 22 of the powertransmission circuit unit 7 so that only the second energy storagedevice 6, out of the first energy storage device 5 and the second energystorage device 6, is charged with the generated power corresponding tothe target value.

In the vehicle driving request state (in the state where the requireddriving force is not zero), the control device 8 determines therespective shares of the required driving force of the entire vehiclethat are taken on by the electric motor 3 and the internal combustionengine 2 in accordance with the required driving force of the entirevehicle, the detected value of the first SOC, and so on.

In this case, the respective shares for the electric motor 3 and theinternal combustion engine 2 are determined so that, basically, all or alarge portion of the required driving force is taken on by the internalcombustion engine 2 and the electric motor 3 serves in an auxiliaryrole.

The control device 8 causes the internal combustion engine operationcontroller 31 to perform control so that the motive power (outputtorque) of the internal combustion engine 2 is equal to motive powerincluding the motive power corresponding to the share of the requireddriving force for the internal combustion engine 2 and the motive powernecessary for the power generation operation of the electric generator4, and also causes the clutch controller 33 to control the clutch 11 toenter the connected state.

Further, the control device 8 determines the required output DM_dmd ofthe electric motor 3 so that the share of the required driving force forthe electric motor 3 is satisfied by the motive power generated throughthe power-running operation of the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverter 23 of the power transmission circuit unit 7 to supply powerfrom only the first energy storage device 5 to the electric motor 3 inaccordance with a pre-created map illustrated in FIG. 16 on the basis ofthe required output DM_dmd and the detected value of the SOC of thefirst energy storage device 5 (i.e., the first SOC).

In the vehicle braking request state (in the state where the requiredbraking force is not zero), the control device 8 determines therespective shares of the required braking force of the entire vehiclefor the electric motor 3 and the brake device. In this case, the controldevice 8 determines the respective shares for the electric motor 3 andthe brake device on the basis of the magnitude of the required brakingforce, the detected value of the first SOC, and so on so as to basicallymaximize the share of the required braking force for the electric motor3.

Then, the control device 8 causes the brake controller 34 to control thebrake device in accordance with the share of the required braking forcefor the brake device.

Further, the control device 8 determines the required amount ofregeneration G_dmd of the electric motor 3 so that the share of therequired braking force for the electric motor 3 is satisfied by theregenerative braking force generated through the regenerative operationof the electric motor 3.

Then, the control device 8 causes the power transmission controller 32to control the inverter 21 on the electric motor 3 side and the voltageconverters 23 and 24 of the power transmission circuit unit 7 to chargeeither or both of the first energy storage device 5 and the secondenergy storage device 6 with the regenerative power output from theelectric motor 3 in accordance with a pre-created map illustrated inFIG. 18 on the basis of the required amount of regeneration G_dmd andthe detected value of the first SOC. In this embodiment, the primaryenergy storage device to be charged with the regenerative power in thesecond CS mode is the second energy storage device 6.

Control Process During Power-Running Operation in Second CS Mode

A control process executed by the power transmission controller 32during the power-running operation of the electric motor 3 in the secondCS mode will be described in detail hereinafter with reference to FIGS.16 and 17.

FIG. 16 illustrates a map depicting how the output demand for the amountof electricity to be supplied (the amount of power supplied) to theelectric motor 3 is shared by the first energy storage device 5 and thesecond energy storage device 6 in the second CS mode in accordance withthe required output DM_dmd of the electric motor 3 and the first SOC.

In FIG. 16, a diagonally hatched area represents an area where all theamount of power supplied to the electric motor 3 is taken on by thefirst energy storage device 5. On the map illustrated in FIG. 16,DM_max3 is a maximum value of the required output DM_dmd in the secondCS mode. The maximum value DM_max1 is a constant value.

In the control process during the power-running operation of theelectric motor 3 in the second CS mode, as illustrated in FIG. 16, theamount of power supplied to the electric motor 3 is always taken on onlyby the first energy storage device 5 within the entire range between theCD→CS switching threshold B1_mc1 (see FIG. 2) and the CS→CD switchingthreshold B1_mc2 (see FIG. 2) for the first SOC. In the second CS mode,accordingly, power supply from the second energy storage device 6 to theelectric motor 3 is disabled.

The control process for the power transmission controller 32 during thepower-running operation of the electric motor 3 in the second CS mode issequentially executed in a predetermined control process cycle inaccordance with a flowchart illustrated in FIG. 17.

In STEP91, the power transmission controller 32 acquires the requiredoutput DM_dmd. Then, in STEP92, the power transmission controller 32controls the voltage converter 23 and the inverter 21 of the powertransmission circuit unit 7 so that the output P1 of the first energystorage device 5 matches the amount of power supplied corresponding tothe required output DM_dmd.

The control process during the power-running operation of the electricmotor 3 in the second CS mode is executed in the way described above. Inthis control process, power supply from the second energy storage device6 to the electric motor 3 is disabled. This can quickly restore the SOCof the second energy storage device 6 with the generated power of theelectric generator 4.

Control Process During Regenerative Operation in Second CS Mode

Next, a control process executed by the power transmission controller 32during the regenerative operation of the electric motor 3 in the secondCS mode will be described in detail hereinafter with reference to FIGS.18 and 19.

FIG. 18 is a map that defines how the regenerative power output by theelectric motor 3 during the regenerative operation in the second CS modeis shared in order to charge the first energy storage device 5 and thesecond energy storage device 6 in accordance with the required amount ofregeneration G_dmd of the electric motor 3 and the first SOC (the firstSOC in the range between the CD→CS switching threshold B1_mc1 and theCS→CD switching threshold B1_mc2).

In FIG. 18, diagonally hatched areas represent areas where all or partof the regenerative power generated by the electric motor 3 is used tocharge the first energy storage device 5, and a shaded area representsan area where all or part of the regenerative power is used to chargethe second energy storage device 6.

On the map illustrated in FIG. 18, G_max3 is a maximum value of therequired amount of regeneration G_dmd in the second CS mode. The maximumvalue G_max3 is a constant value.

A control process for the power transmission controller 32 during theregenerative operation of the electric motor 3 in the second CS mode issequentially executed in a predetermined control process cycle by usingthe map illustrated in FIG. 18 in accordance with a flowchartillustrated in FIG. 19.

In STEP101, the power transmission controller 32 acquires the requiredamount of regeneration G_dmd and a detected value of the first SOC.

Then, in STEP102, the power transmission controller 32 determineswhether or not the required amount of regeneration G_dmd is less than orequal to a predetermined threshold G_th5.

In this embodiment, the threshold G_th5 is set in accordance with thefirst SOC. Specifically, as illustrated in the example in FIG. 18, thethreshold G_th5 is set to a predetermined constant value when the firstSOC is an SOC less than or equal to a predetermined value B1f that isslightly smaller than the threshold B1_th1. The constant value isdetermined to be a comparatively small value so as to allow the firstenergy storage device 5 to be charged at a low rate (low speed) tominimize the progression of deterioration of the first energy storagedevice 5.

When the first SOC is larger than the predetermined value B1f, thethreshold G_th5 is set to successively decrease from the constant valueto zero (reach zero at the threshold B1_th1) in accordance with theincrease in the first SOC. When the first SOC is an SOC greater than orequal to the threshold B1_th1, the threshold G_th5 is kept at zero.

The determination result of STEP102 is affirmative for the lowerdiagonally hatched area illustrated in FIG. 18. In this situation, inSTEP103, the power transmission controller 32 controls the voltageconverter 23 and the inverter 21 of the power transmission circuit unit7 so that the input Pc1 of the first energy storage device 5 matches theamount of charging power corresponding to the required amount ofregeneration G_dmd. In this case, the voltage converter 24 on the secondenergy storage device 6 side is controlled to block charging of thesecond energy storage device 6.

For additional explanation, when the detected value of the first SOC isgreater than or equal to the threshold B1_th1, the threshold G_th5 iszero and thus no affirmative determination is made in STEP102. Thus, inthis case, the processing of STEP103 is not executed.

If the determination result of STEP102 is negative, then, in STEP104,the power transmission controller 32 determines whether or not therequired amount of regeneration G_dmd is less than or equal to apredetermined threshold G_th6.

In this embodiment, the threshold G_th6 is set in accordance with thefirst SOC in a way similar to that for the threshold G_th5 in STEP102described above. Specifically, as illustrated in the example in FIG. 18,when the first SOC is an SOC greater than or equal to the thresholdB1_th1, the threshold G_th6 is set to a predetermined constant value.The constant value is set so that the amount of charging powercorresponding to the difference between the threshold G_th6 and themaximum value G_max3 of the required amount of regeneration G_dmd(=G_max3−G_th6) matches the amount of charging power corresponding tothe maximum value of the threshold G_th5 (the value of the thresholdG_th5 when the first SOC is less than or equal to the threshold B1f)(the amount of charging power by which the first energy storage device 5can be charged at a low rate).

When the first SOC is smaller than the threshold B1_th1, the thresholdG_th6 is set to increase to the maximum value G_max3 (reach the maximumvalue G_max3 at the threshold B1f) in accordance with the decrease inthe first SOC in a pattern similar to the pattern in which the thresholdG_th5 changes. When the first SOC is less than or equal to the thresholdB1f, the threshold G_th6 is maintained at the maximum value G_max3.

The thresholds G_th5 and G_th6 are set so that, within the range of B1fto B1_th1 of the first SOC, the thresholds G_th5 and G_th6 are set sothat the sum of the amount of charging power corresponding to thedifference between the maximum value G_max1 and the threshold G_th6(=G_max3−G_th6) and the amount of charging power corresponding to thethreshold G_th5 matches the amount of charging power corresponding tothe maximum value of the threshold G_th5 (the amount of charging powerby which the first energy storage device 5 can be charged at a lowrate).

The determination result of STEP104 is affirmative for the shaded areaillustrated in FIG. 18. In this situation, in STEP105, the powertransmission controller 32 controls the voltage converters 23 and 24 andthe inverter 21 of the power transmission circuit unit 7 so that theinput Pc1 of the first energy storage device 5 matches the amount ofcharging power corresponding to the threshold G_th5 and so that theinput Pc2 of the second energy storage device 6 matches the amount ofcharging power obtained by subtracting the input Pc1 of the first energystorage device 5 from the amount of charging power corresponding to therequired amount of regeneration G_dmd.

On the other hand, the determination result of STEP104 is negative forthe upper diagonally hatched area illustrated in FIG. 18. In thissituation, in STEP106, the power transmission controller 32 controls thevoltage converters 23 and 24 and the inverter 21 of the powertransmission circuit unit 7 so that the input Pc2 of the second energystorage device 6 matches the amount of charging power corresponding tothe difference between the thresholds G_th5 and G_th6 (=G_th6−G_th5) andso that the input Pc1 of the first energy storage device 5 matches theamount of charging power obtained by subtracting the input Pc2 of thesecond energy storage device 6 from the amount of charging powercorresponding to the required amount of regeneration G_dmd.

For additional explanation, when the first SOC is less than or equal tothe predetermined value B1f, the threshold G_th6 matches the maximumvalue G_max1 and thus no negative determination is made in STEP104.Thus, in this case, the processing of STEP106 is not executed.

The control process during the regenerative operation of the electricmotor 3 in the second CS mode is executed in the way described above. Inthis control process, when the detected value of the first SOC is largerthan the threshold B1_th1, all or a large portion of the regenerativepower is used to charge the second energy storage device 6. Thus, theSOC of the second energy storage device 6 may be effectively restoredwith regenerative power.

In the second CS mode, the second energy storage device 6 is chargedwith generated power produced by the electric generator 4, except duringthe regenerative operation of the electric motor 3. Both the generatedpower and the regenerative power can be used to quickly restore the SOCof the second energy storage device 6 toward the CS2-÷CS1 switchingthreshold B2_mc2.

When the detected value of the first SOC is smaller than the thresholdB1_th1, the first energy storage device 5 is preferentially charged withregenerative power within the range where the required amount ofregeneration G_dmd is less than or equal to the threshold G_th5.Further, when the detected value of the first SOC is larger than thepredetermined value B1f, the first energy storage device 5 is chargedwith regenerative power within the range where the required amount ofregeneration G_dmd is larger than the threshold G_th6. The amount ofcharging power of the first energy storage device 5 is limited to avalue less than or equal to the amount of charging power correspondingto the maximum value of the threshold G_th5. This can suppress areduction in the first SOC in the second CS mode while minimizing theprogression of deterioration of the first energy storage device 5.

A detailed description has been made of the control process for thecontrol device 8 in this embodiment.

In this embodiment, the range of the first SOC (the range of B1a (%) toBib (%) illustrated in FIG. 2) used for supplying power to the electricmotor 3 in the CD mode is larger than the range of the second SOC (therange of B2a (%) to B2b (%) illustrated in FIG. 2) used for supplyingpower to the electric motor 3 in the CD mode. Further, the range of thesecond SOC (the range of B2b (%) to B2c (%) illustrated in FIG. 2) usedfor supplying power to the electric motor 3 in the CS mode is largerthan the range of the first SOC (part of the range less than or equal toBib (%) illustrated in FIG. 2) used for supplying power to the electricmotor 3 in the CS mode.

Furthermore, power to be supplied to the electric generator 4, whichserves as a starter actuator, when the internal combustion engine 2 isstarted in the CS mode is reserved in only the second energy storagedevice 6.

For this reason, a large portion of the power (stored energy) in thefirst energy storage device 5 with relatively high energy density can beutilized as power to be supplied to the electric motor 3 in the CD mode.As a result, the period during which power can be supplied from thefirst energy storage device 5 to the electric motor 3 in the CD mode,and therefore the drivable range of the vehicle in the CD mode in whichfuel consumption of the internal combustion engine 2 does not occur oris suppressed, can be maximized. In addition, the environmentalperformance of the motive power system 1 is improved.

In addition, part of the power in the second energy storage device 6(the stored energy within the range of B2a (%) to B2b (%) illustrated inFIG. 2) is usable as dedicated power to be supplied to the electricmotor 3 in the CD mode. This allows power to be supplied from the secondenergy storage device 6 with relatively high power density to theelectric motor 3 in an auxiliary manner, as necessary. Thus, the runningperformance of the vehicle (the driving performance of the drive wheelDW) in the CD mode can be enhanced.

In the first CS mode within the CS mode, the second energy storagedevice 6 can be used as the primary power supply for the electric motor3. Thus, the motive power of the electric motor 3 can be transmitted tothe drive wheel DW in an auxiliary manner with high responsivity to achange in the required driving force of the vehicle. As a result, therunning performance of the vehicle (the driving performance of the drivewheel DW) in the first CS mode can be enhanced.

In addition, part of the power in the first energy storage device 5(part of the range less than or equal to Bib (%) illustrated in FIG. 2)is usable as power to be supplied to the electric motor 3 in the CSmode. This allows power to be supplied, in particular, in the second CSmode, from the first energy storage device 5, instead of the secondenergy storage device 6, to the electric motor 3, as necessary. This caneliminate power supply from the second energy storage device 6 to theelectric motor 3 in the second CS mode. Thus, restoration of the SOC ofthe second energy storage device 6 in the second CS mode can beaccelerated.

In this embodiment, furthermore, in the second CS mode, the generatedpower of the electric generator 4 is used to charge only the secondenergy storage device 6. Part of the power used to charge the secondenergy storage device 6 in this manner is transferred from the secondenergy storage device 6 to the first energy storage device 5 in thefirst CS mode. In this case, in the first CS mode, the first energystorage device 5 can be charged stably at a low rate. This can minimizethe progression of deterioration of the first energy storage device 5.

FIG. 20 is a graph exemplifying schematic changes in the respective SOCsof the first energy storage device 5 and the second energy storagedevice 6 over time during the travel of the vehicle.

The period up to time t1 is the period of the CD mode. During thisperiod, the first SOC decreases basically. The second SOC changes inresponse to appropriate discharging and charging of the second energystorage device 6.

When the first SOC decreases to the CD→CS switching threshold B1_mc1 attime t1, the mode of the control process for the control device 8 isswitched to the first CS mode. The period from time t1 to time t2 is theperiod of the first CS mode. During the period of the first CS mode, thesecond SOC basically decreases in response to power supply to either orboth of the first energy storage device 5 and the electric motor 3. Thefirst SOC is gradually restored in response to appropriate charging ofthe first energy storage device 5 with power supplied from the secondenergy storage device 6.

When the second SOC decreases to the CS1→CS2 switching threshold B2_mc1at time t2, the mode of the control process for the control device 8 isswitched to the second CS mode. The period from time t2 to time t3 isthe period of the second CS mode. During the period of the second CSmode, the second SOC increases in response to charging of the secondenergy storage device 6 with generated power and regenerative power.

In the second CS mode, the first SOC decreases in a situation wherepower is supplied from the first energy storage device 5 to the electricmotor 3. In the second CS mode, however, since the second SOC is quicklyrestored by the generated power and the regenerative power, power supplyfrom the first energy storage device 5 to the electric motor 3 is notfrequently required in most cases. Thus, the reduction in the first SOCin the second CS mode does not so often occur.

When the second SOC is restored to the CS2→CS1 switching thresholdB2_mc2 at time t3, the mode of the control process for the controldevice 8 is switched to the first CS mode again. The period from time t3to time t4 is the period of the first CS mode. During the period of thefirst CS mode, as in the period from time t1 to time t2, the second SOCdecreases in response to power supply to either or both of the firstenergy storage device 5 and the electric motor 3, and the first SOC isgradually restored.

In the illustrated example, at time t4, the first SOC is restored to theCS→CD switching threshold B1_mc2. In response to the restoration, themode of the control process for the control device 8 is returned to theCD mode.

As described above, in the CS mode subsequent to the CD mode, the firstSOC can be gradually restored basically by alternately repeating thefirst CS mode and the second CS mode. As a result, the travel of thevehicle can be restarted in the CD mode in which only the motive powerof the electric motor 3 is used to drive the drive wheel DW.

Modifications

There will now be described some modifications related to the embodimentdescribed above.

In the embodiment described above, the supply of power for causing theelectric generator 4 to operate as a starter actuator is taken on onlyby the second energy storage device 6. Alternatively, part of the powerto be supplied to the electric generator 4 may also be taken on by thefirst energy storage device 5. In this case, it is desirable that theload on the first energy storage device 5 be less than the load on thesecond energy storage device 6.

For utmost utilization of the power in the first energy storage device 5in the CD mode, it is desirable that all the power to be supplied to theelectric generator 4 be taken on by the second energy storage device 6.

In the embodiment described above, furthermore, power is supplied fromonly the first energy storage device 5 to the electric motor 3(discharge from the second energy storage device 6 is disabled) duringthe power-running operation of the electric motor 3 in the second CSmode. However, for example, if the required output DM_dmd is large, theamount of power supplied corresponding to part of the required outputDM_dmd may be supplied from the second energy storage device 6 to theelectric motor 3.

In the description of the embodiment described above, a transportationapparatus including the motive power system 1 is a hybrid vehicle, byway of example. The transportation apparatus is not limited to a vehicleand may be a ship, a railway carriage, or any other apparatus. Thedriven load may not necessarily be the drive wheel DW of a vehicle. Theactuator may be an actuator other than an electric motor.

A motive power system according to an aspect of the embodimentsdisclosed herein includes a first energy storage device, a second energystorage device having a higher power density and a lower energy densitythan the first energy storage device, an actuator that outputs motivepower for driving a driven load in response to power supplied from atleast one of the first energy storage device and the second energystorage device, an internal combustion engine that outputs motive powerfor driving the driven load, a power transmission circuit unit having afunction of performing power transmission among the first energy storagedevice, the second energy storage device, and the actuator, and acontrol device having a function of controlling the power transmissioncircuit unit by using a charge-depleting mode and a charge-sustainingmode, the charge-depleting mode being a mode in which only the motivepower of the actuator, out of the internal combustion engine and theactuator, is usable as motive power for driving the driven load, thecharge-sustaining mode being a mode in which the motive power of theinternal combustion engine and the motive power of the actuator areusable as motive power for driving the driven load, wherein the controldevice is configured to execute a process for controlling the powertransmission circuit unit so that, among a range of a charge rate of thefirst energy storage device and a range of a charge rate of the secondenergy storage device that are usable for power supply to the actuatorin the charge-depleting mode, the range of the charge rate of the firstenergy storage device is larger than the range of the charge rate of thesecond energy storage device (a first aspect of the embodiments).

In the embodiments, the “power transmission circuit unit” having afunction of performing power transmission among the first energy storagedevice, the second energy storage device, and the actuator refers to the“power transmission circuit unit” having at least a function capable ofcontrolling the amount of power supplied from each of the first energystorage device and the second energy storage device to the actuator, orhaving, in addition to this function, a function capable of controllingselective switching of the source and destination of power among thefirst energy storage device, the second energy storage device, and theactuator.

Further, the term “amount of power supplied” refers to the amount ofelectricity supplied from the first energy storage device or the secondenergy storage device to the target to which power is supplied. In thiscase, the target to which power is supplied is not limited to theactuator and may be an energy storage device (the first energy storagedevice or the second energy storage device). The “amount of electricity”or the “amount of power supplied” is expressed as an amount ofelectrical energy per unit time (e.g., a value of power) or an amount ofcharge per unit time (e.g., a value of current), for example.

According to the first aspect of the embodiments, among ranges of therespective charge rates of the first energy storage device and thesecond energy storage device used for supplying power to the actuator inthe CD mode, the range of the charge rate of the first energy storagedevice is larger than the charge rate of the second energy storagedevice.

In the CD mode, accordingly, the first energy storage device havingrelatively high energy density can be used as the primary power supplyfor the actuator to supply power to the actuator. This can maximize theperiod during which the driven load can be driven with only the motivepower of the actuator. That is, in the CD mode in which fuel consumptionof the internal combustion engine does not occur or is suppressed, theperiod during which the driven load can be driven is increased and theenvironmental performance of the motive power system is improved.

In the CD mode, furthermore, part of the power (stored energy) in thesecond energy storage device with relatively high power density can alsobe supplied to the actuator in an auxiliary manner, as necessary. Thisallows the amount of power supplied to the actuator to be changed withhigh responsivity in response to a request for changing the operation ofthe driven load. In addition to this, it is possible to moderate thechange in the amount of power supplied from the first energy storagedevice to the actuator and thus to suppress the progression ofdeterioration of the first energy storage device.

In this manner, even in a situation where the power in the second energystorage device is used in an auxiliary manner, fuel consumption of theinternal combustion engine is suppressed. In addition, since theprogression of deterioration of the first energy storage device isachievable, the power in the first energy storage device, which isusable for a long term, is increased. Thus, the environmentalperformance of the motive power system can be improved accordingly.

Thus, according to the first aspect of the embodiments, at least in theCD mode, accurate driving of the driven load is achievable byappropriately using the power in two energy storage devices havingdifferent characteristics.

In the first aspect of the embodiments, preferably, the control deviceis configured to execute a process for controlling the powertransmission circuit unit so that, among a range of a charge rate of thefirst energy storage device and a range of a charge rate of the secondenergy storage device that are usable for power supply to the actuatorin the charge-sustaining mode, the range of the charge rate of thesecond energy storage device is larger than the range of the charge rateof the first energy storage device (a second aspect of the embodiments).

According to this configuration, in the CS mode, the first energystorage device with relatively high power density can be used as theprimary power supply for the actuator to supply power to the actuator.

In the CS mode, the internal combustion engine may be used as theprimary source of motive power for driving the driven load, and theactuator may be used as an auxiliary source of motive power. The CS modethus requires only a small total amount of power to operate theactuator, compared with the CD mode. This can ensure that the periodduring which the period during which the actuator can be caused tooperate appropriately can be sufficient even when the second energystorage device with lower energy density than the first energy storagedevice is used as the primary power supply for the actuator in the CSmode.

In addition, power supply from the second energy storage device withrelatively high power density allows the actuator to operate as anauxiliary source of motive power for driving the driven load. Thus, theamount of power supplied to the actuator can be changed with highresponsivity in response to a request for changing the operation of thedriven load.

Accordingly, when the motive power system outputs a high driving forceto the driven load, such power supply from the second energy storagedevice allows the actuator to output auxiliary power to the driven load.This can not only suppress excessive fuel consumption of the internalcombustion engine but also reduce the displacement of the internalcombustion engine.

Furthermore, because of the higher power density than the first energystorage device, the second energy storage device is superior to thefirst energy storage device in the resistance to charge or discharge forwhich high responsivity is required. Accordingly, deterioration of thefirst energy storage device can further be suppressed.

In the CS mode, only a small total amount of power is required to besupplied from the first energy storage device to the actuator. Thismakes it possible to further increase the range of the charge rate ofthe first energy storage device which is usable in the CD mode.

Thus, the period during which power can be supplied from the firstenergy storage device to the actuator in the CD mode can further beincreased. That is, in the CD mode in which fuel consumption of theinternal combustion engine does not occur or is suppressed, the periodduring which the driven load can be driven is increased and theenvironmental performance of the motive power system is improved.

In the first or second aspect of the embodiments, preferably, the powertransmission circuit unit is configured to be capable of supplying powerfrom at least one of the first energy storage device and the secondenergy storage device to a starter actuator that outputs a driving forcefor starting the internal combustion engine, and the control device isconfigured to further have a function of controlling the powertransmission circuit unit so that an amount of power supplied from thesecond energy storage device to the starter actuator is larger than anamount of power supplied from the first energy storage device to thestarter actuator when the internal combustion engine is started (a thirdaspect of the embodiments).

According to this configuration, when the internal combustion engine isstarted, the second energy storage device, out of the first energystorage device and the second energy storage device, is used as theprimary power supply to supply power to the starter actuator.

Thus, the share of the total amount of power required to start theinternal combustion engine that is taken on by the first energy storagedevice can be lower than the share taken on by the second energy storagedevice. This can further increase the range of the charge rate of thefirst energy storage device which is usable in the CD mode.

In addition, the supply of comparatively large power to the starteractuator is instantaneously required for the start of the internalcombustion engine. It is thus preferable that a larger amount of powerbe supplied from the second energy storage device to the starteractuator than from the first energy storage device in order to minimizethe progression of deterioration of the first energy storage device andthe second energy storage device.

Furthermore, the second energy storage device with higher power densitythan the first energy storage device typically has a smaller internalresistance (impedance) than the first energy storage device, and canensure that an amount of power required to start the internal combustionengine can be supplied to the starter actuator even in the state wherethe charge rate is low. According to the third aspect of theembodiments, thus, the proportion of power not used to start theinternal combustion engine in the total amount of power in the firstenergy storage device and the second energy storage device can beincreased.

Thus, it is possible to further increase the period during which powercan be supplied from the first energy storage device to the actuator inthe CD mode. That is, in the CD mode in which fuel consumption of theinternal combustion engine does not occur or is suppressed, the periodduring which the driven load can be driven is increased and theenvironmental performance of the motive power system is improved.

In the third aspect of the embodiments, preferably, the control deviceis configured to control the power transmission circuit unit to, whenthe internal combustion engine is started, supply power from only thesecond energy storage device, out of the first energy storage device andthe second energy storage device, to the starter actuator (a fourthaspect of the embodiments).

According to this configuration, the share of the total amount of powerrequired to start the internal combustion engine that is taken on by thefirst energy storage device is zero (minimum). This eliminates the needfor the first energy storage device to reserve power to be supplied tothe starter actuator. This can maximize the range of the charge rate ofthe first energy storage device which is usable in the CD mode. Thus,the period during which power can be supplied from the first energystorage device to the actuator in the CD mode can be maximized. That is,in the CD mode in which fuel consumption of the internal combustionengine does not occur or is suppressed, the period during which thedriven load can be driven is increased and the environmental performanceof the motive power system is improved.

In addition, instantaneous power supply to the starter actuator, whichis required to start the internal combustion engine, is undertaken bythe second energy storage device. This can favorably suppress theprogression of deterioration of the first energy storage device.

In the first to fourth aspects of the embodiments, preferably, thecontrol device is configured to selectively execute the process for thecharge-depleting mode and the process for the charge-sustaining mode inaccordance with the charge rate of the first energy storage device (afifth aspect of the embodiments).

This configuration enables switching between the CD mode and the CS modein accordance with the charge rate of the first energy storage devicewhich stores a substantial portion of the total stored energy that canbe supplied from the first energy storage device and the second energystorage device to the actuator. This results in the switching beingperformed at appropriate timing.

In particular, it is preferable to control the power transmissioncircuit unit so that, in terms of reduction in deterioration of thefirst energy storage device and the second energy storage device, thefirst energy storage device performs a continuous discharge operationand the second energy storage device performs instantaneous discharge orcharge operation while making use of the respective characteristics ofthe first energy storage device and the second energy storage device. Inthis case, switching between the CD mode and the CS mode in accordancewith the charge rate of the first energy storage device, whichsubstantially monotonically decreases, rather than in accordance withthe charge rate of the second energy storage device, which is morelikely to frequently increase or decrease, prevents frequent repetitionof start and stop of the internal combustion engine.

In the first to fifth aspects of the embodiments, preferably, thecontrol device is configured to keep the internal combustion engine atrest in the charge-depleting mode (a sixth aspect of the embodiments).

In the CD mode in the first to fifth aspects of the embodiments, theinternal combustion engine is not used as a source of motive power forthe driven load. However, the internal combustion engine can be used as,for example, a source of motive power for an electric generator forgenerating power used to charge the first energy storage device or thesecond energy storage device, such as for series-hybrid travel. In thiscase, however, exhaust gases are generated from the internal combustionengine in the CD mode.

In the sixth aspect of the embodiments, in contrast, the driven load canbe driven with only the motive power of the actuator in the CD modewithout generation of exhaust gases from the internal combustion engine.In particular, the motive power system according to the embodimentsdisclosed herein, which includes the first energy storage device withrelatively high energy density and the second energy storage device withrelatively high power density, ensures that the period during which thedriven load can be driven can be sufficient without the generation ofpower by the electric generator using the motive power of the internalcombustion engine in the CD mode.

Further, according to another aspect of the embodiments disclosed hereinmay provide a motive power system including a first energy storagedevice, a second energy storage device having a higher power density anda lower energy density than the first energy storage device, an actuatorthat outputs motive power for driving a driven load in response to powersupplied from at least one of the first energy storage device and thesecond energy storage device, an internal combustion engine that outputsmotive power for driving the driven load, a power transmission circuitunit having a function of performing power transmission among the firstenergy storage device, the second energy storage device, and theactuator, and a control device having a function of controlling thepower transmission circuit unit by using a charge-depleting mode and acharge-sustaining mode, the charge-depleting mode being a mode in whichonly the motive power of the actuator, out of the internal combustionengine and the actuator, is usable as motive power for driving thedriven load, the charge-sustaining mode being a mode in which the motivepower of the internal combustion engine and the motive power of theactuator are usable as motive power for driving the driven load, whereinthe control device is configured to execute a process for controllingthe power transmission circuit unit so that, among a range of a chargerate of the first energy storage device and a range of a charge rate ofthe second energy storage device that are usable for power supply to theactuator in the charge-sustaining mode, the range of the charge rate ofthe second energy storage device is larger than the range of the chargerate of the first energy storage device (a seventh aspect of theembodiments).

In the seventh aspect of the embodiments, in the CS mode, among rangesof the respective charge rates of the first energy storage device andthe second energy storage device used for supplying power to theactuator, the range of the charge rate of the second energy storagedevice is larger than the range of the charge rate of the first energystorage device.

Thus, in the CS mode, the first energy storage device with relativelyhigh power density can be used as the primary power supply for theactuator to supply power to the actuator.

As described above with reference to the second aspect of theembodiments, in the CS mode, the internal combustion engine may be usedas the primary source of motive power for driving the driven load, andthe actuator may be used as an auxiliary source of motive power. Thiscan ensure that the period during which the actuator can be caused tooperate appropriately can be sufficient even when the second energystorage device with lower energy density than the first energy storagedevice is used as the primary power supply for the actuator in the CSmode.

In addition, power supply from the second energy storage device withrelatively high power density allows the actuator to operate as anauxiliary source of motive power for driving the driven load. Thus, theamount of power supplied to the actuator can be changed with highresponsivity in response to a request for changing the operation of thedriven load.

Accordingly, when the motive power system outputs a high driving forceto the driven load, such power supply from the second energy storagedevice allows the actuator to output auxiliary power to the driven load.This can not only suppress excessive fuel consumption of the internalcombustion engine but also reduce the displacement of the internalcombustion engine.

Furthermore, because of the higher power density than the first energystorage device, the second energy storage device is superior to thefirst energy storage device in the resistance to charge or discharge forwhich high responsivity is required. Accordingly, deterioration of thefirst energy storage device can further be suppressed.

In the CS mode, only a small total amount of power is required to besupplied from the first energy storage device to the actuator. Thismakes it possible to further increase the range of the charge rate ofthe first energy storage device which is usable in the CD mode.

Thus, the period during which power can be supplied from the firstenergy storage device to the actuator in the CD mode can further beincreased. That is, in the CD mode in which fuel consumption of theinternal combustion engine does not occur or is suppressed, the periodduring which the driven load can be driven is increased and theenvironmental performance of the motive power system is improved.

Thus, according to the seventh aspect of the embodiments, at least inthe CS mode, accurate driving of the driven load is achievable byappropriately using the power in two energy storage devices havingdifferent characteristics.

In the first to seventh aspects of the embodiments described above, thedriven load may be implemented as a drive wheel of a vehicle, forexample. The actuator may be implemented as an electric motor, forexample. The power transmission circuit unit may have a configurationthat includes a voltage converter that converts an output voltage of atleast one of the first energy storage device and the second energystorage device and outputs the resulting voltage, and an inverter thatconverts direct-current power input from the first energy storagedevice, the second energy storage device, or the voltage converter intoalternating-current power and supplies the alternating-current power tothe actuator.

Further, a transportation apparatus according to an aspect of theembodiments disclosed herein includes the motive power system accordingto the first to seventh aspects of the embodiments (an eighth aspect ofthe embodiments). This transportation apparatus is implementable as atransportation apparatus that achieves the advantages described abovewith reference to the first to seventh aspects of the embodimentsdisclosed herein.

Further, a power transmission method for a motive power system accordingto an aspect of the embodiments disclosed herein is a power transmissionmethod for a motive power system, for performing power transmissionamong a first energy storage device, a second energy storage device, andan actuator by using a charge-depleting mode and a charge-sustainingmode in the motive power system, the motive power system including thefirst energy storage device, the second energy storage device, theactuator, and an internal combustion engine, the second energy storagedevice having a higher power density and a lower energy density than thefirst energy storage device, the actuator outputting motive power fordriving a driven load in response to power supplied from at least one ofthe first energy storage device and the second energy storage device,the internal combustion engine outputting motive power for driving thedriven load, the charge-depleting mode being a mode in which only themotive power of the actuator, out of the internal combustion engine andthe actuator, is usable as motive power for driving the driven load, thecharge-sustaining mode being a mode in which the motive power of theinternal combustion engine and the motive power of the actuator areusable as motive power for driving the driven load. The powertransmission method includes performing the power transmission so that,among a range of a charge rate of the first energy storage device and arange of a charge rate of the second energy storage device that areusable for power supply to the actuator in the charge-depleting mode,the range of the charge rate of the first energy storage device islarger than the range of the charge rate of the second energy storagedevice (a ninth aspect of the embodiments).

Alternatively, a power transmission method for a motive power systemaccording to an aspect of the embodiments disclosed herein is a powertransmission method for a motive power system, for performing powertransmission among a first energy storage device, a second energystorage device, and an actuator by using a charge-depleting mode and acharge-sustaining mode in the motive power system, the motive powersystem including the first energy storage device, the second energystorage device, the actuator, and an internal combustion engine, thesecond energy storage device having a higher power density and a lowerenergy density than the first energy storage device, the actuatoroutputting motive power for driving a driven load in response to powersupplied from at least one of the first energy storage device and thesecond energy storage device, the internal combustion engine outputtingmotive power for driving the driven load, the charge-depleting modebeing a mode in which only the motive power of the actuator, out of theinternal combustion engine and the actuator, is usable as motive powerfor driving the driven load, the charge-sustaining mode being a mode inwhich the motive power of the internal combustion engine and the motivepower of the actuator are usable as motive power for driving the drivenload. The power transmission method includes performing the powertransmission so that, among a range of a charge rate of the first energystorage device and a range of a charge rate of the second energy storagedevice that are usable for power supply to the actuator in thecharge-sustaining mode, the range of the charge rate of the secondenergy storage device is larger than the range of the charge rate of thefirst energy storage device (a tenth aspect of the embodiments).

The ninth aspect of the embodiments disclosed herein can achieveadvantages similar to those of the first aspect of the embodimentsdisclosed herein. The tenth aspect of the embodiments disclosed hereincan achieve advantages similar to those of the seventh aspect of theembodiments disclosed herein.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A motive power system comprising: a first energystorage having a first power density and a first energy density; asecond energy storage having a second power density higher than thefirst power density, and a second energy density lower than the firstenergy density; an actuator to provide motive force to a load withelectric power supplied from at least one of the first energy storageand the second energy storage; an internal combustion engine to providemotive force to the load; a power transmission circuit via which theactuator is connected to the first energy storage and to the secondenergy storage to supply electric power to the actuator; and circuitryconfigured to control the power transmission circuit and the internalcombustion engine such that only the actuator provides motive force tothe load in a charge-depleting mode and such that the internalcombustion engine and the actuator provide motive force to the load in acharge-sustaining mode; and control the power transmission circuit inthe charge-depleting mode such that the first energy storage supplies tothe actuator a first electric energy that is stored in the first energystorage with a first charge rate range and the second energy storagesupplies to the actuator a second electric energy that is stored in thesecond energy storage with a second charge rate range, the first chargerate range being larger than the second charge rate range.
 2. The motivepower system according to claim 1, wherein the circuitry is configuredto control the power transmission circuit in the charge-sustaining modesuch that the first energy storage supplies to the actuator an electricenergy that is stored in the first energy storage with one charge raterange and the second energy storage supplies to the actuator an electricenergy that is stored in the second energy storage with an anothercharge rate range, the another charge rate range being larger than theone charge rate range.
 3. The motive power system according to claim 1,wherein the power transmission circuit is configured to supply powerfrom at least one of the first energy storage and the second energystorage to a starter actuator that outputs a driving force for startingthe internal combustion engine, and wherein the circuitry is configuredto control the power transmission circuit so that an amount of powersupplied from the second energy storage to the starter actuator islarger than an amount of power supplied from the first energy storage tothe starter actuator when the internal combustion engine is started. 4.The motive power system according to claim 3, wherein the circuitry isconfigured to control the power transmission circuit to, when theinternal combustion engine is started, supply power from only the secondenergy storage, out of the first energy storage and the second energystorage, to the starter actuator.
 5. The motive power system accordingto claim 1, wherein the circuitry is configured to selectively execute aprocess for the charge-depleting mode and a process for thecharge-sustaining mode in accordance with a charge rate of the firstenergy storage.
 6. The motive power system according to claim 1, whereinthe circuitry is configured to keep the internal combustion engine atrest in the charge-depleting mode.
 7. A motive power system comprising:a first energy storage having a first power density and a first energydensity; a second energy storage having a second power density higherthan the first power density, and a second energy density lower than thefirst energy density; an actuator to provide motive force to a load withelectric power supplied from at least one of the first energy storageand the second energy storage; an internal combustion engine to providemotive force to the load; a power transmission circuit via which theactuator is connected to the first energy storage and to the secondenergy storage to supply electric power to the actuator; and circuitryconfigured to control the power transmission circuit and the internalcombustion engine such that only the actuator provides motive force tothe load in a charge-depleting mode and such that the internalcombustion engine and the actuator provide motive force to the load in acharge-sustaining mode; and control the power transmission circuit inthe charge-sustaining mode such that the first energy storage suppliesto the actuator a first electric energy that is stored in the firstenergy storage with one charge rate range and the second energy storagesupplies to the actuator a second electric energy that is stored in thesecond energy storage with an another charge rate range, the anothercharge rate range being larger than the one charge rate range.
 8. Atransportation apparatus comprising the motive power system according toclaim
 1. 9. A power transmission method for a motive power systemincluding a first energy storage having a first power density and afirst energy density, a second energy storage having a second powerdensity higher than the first power density and a second energy densitylower than the first energy density, an actuator to provide motive forceto a load with electric power supplied from at least one of the firstenergy storage and the second energy storage, and an internal combustionengine to provide motive force to the load, the power transmissionmethod comprising: performing power transmission such that only theactuator provides motive force to the load in a charge-depleting modeand such that the internal combustion engine and the actuator providemotive force to the load in a charge-sustaining mode; and performingpower transmission in the charge-depleting mode such that the firstenergy storage supplies to the actuator a first electric energy that isstored in the first energy storage with a first charge rate range andthe second energy storage supplies to the actuator a second electricenergy that is stored in the second energy storage with a second chargerate range, the first charge rate range being larger than the secondcharge rate range.
 10. The power transmission method according to claim9, further comprising: performing power transmission in thecharge-sustaining mode such that the first energy storage supplies tothe actuator an electric energy that is stored in the first energystorage with one charge rate range and the second energy storagesupplies to the actuator an electric energy that is stored in the secondenergy storage with an another charge rate range, the another chargerate range being larger than the one charge rate range.